/* ========================================================================== 
   CHESTERFIELDER V1 DESIGN SYSTEM
   1. Design Tokens
   2. Reset & Base Styles
   3. Typography
   4. Layout
   5. Reusable Components
   6. Feature-Specific Styles
   7. Utilities
   8. Animations
   9. Responsive & Accessibility Rules
   ========================================================================== */

/* ========================================================================== 
   1. DESIGN TOKENS
   ========================================================================== */

:root {
  /* Brand colors */
  --color-primary-50: #eef2ff;
  --color-primary-100: #e0e7ff;
  --color-primary-200: #c7d2fe;
  --color-primary-300: #a5b4fc;
  --color-primary-400: #818cf8;
  --color-primary-500: #6366f1;
  --color-primary-600: #4f46e5;
  --color-primary-700: #4338ca;
  --color-primary-800: #3730a3;
  --color-primary-900: #312e81;
  --color-primary: var(--color-primary-600);
  --color-primary-hover: var(--color-primary-700);
  --color-primary-active: var(--color-primary-800);
  --color-primary-soft: var(--color-primary-50);

  --color-secondary-50: #ecfeff;
  --color-secondary-100: #cffafe;
  --color-secondary-500: #06b6d4;
  --color-secondary-600: #0891b2;
  --color-secondary-700: #0e7490;
  --color-secondary: var(--color-secondary-600);
  --color-secondary-hover: var(--color-secondary-700);

  --color-accent-50: #fff7ed;
  --color-accent-100: #ffedd5;
  --color-accent-400: #fb923c;
  --color-accent-500: #f97316;
  --color-accent-600: #ea580c;
  --color-accent: var(--color-accent-500);

  /* Semantic colors */
  --color-success-50: #ecfdf5;
  --color-success-100: #d1fae5;
  --color-success-500: #10b981;
  --color-success-600: #059669;
  --color-success-700: #047857;
  --color-success: var(--color-success-600);

  --color-warning-50: #fffbeb;
  --color-warning-100: #fef3c7;
  --color-warning-500: #f59e0b;
  --color-warning-600: #d97706;
  --color-warning-700: #b45309;
  --color-warning: var(--color-warning-600);

  --color-danger-50: #fef2f2;
  --color-danger-100: #fee2e2;
  --color-danger-500: #ef4444;
  --color-danger-600: #dc2626;
  --color-danger-700: #b91c1c;
  --color-danger: var(--color-danger-600);

  --color-info-50: #eff6ff;
  --color-info-100: #dbeafe;
  --color-info-500: #3b82f6;
  --color-info-600: #2563eb;
  --color-info-700: #1d4ed8;
  --color-info: var(--color-info-600);

  /* Neutral palette */
  --color-white: #ffffff;
  --color-black: #0b1020;
  --color-gray-25: #fcfcfd;
  --color-gray-50: #f8fafc;
  --color-gray-100: #f1f5f9;
  --color-gray-200: #e2e8f0;
  --color-gray-300: #cbd5e1;
  --color-gray-400: #94a3b8;
  --color-gray-500: #64748b;
  --color-gray-600: #475569;
  --color-gray-700: #334155;
  --color-gray-800: #1e293b;
  --color-gray-900: #0f172a;
  --color-gray-950: #020617;

  /* Theme aliases: use these throughout components */
  --color-background: #f5f7fb;
  --color-background-subtle: var(--color-gray-50);
  --color-surface: var(--color-white);
  --color-surface-raised: var(--color-white);
  --color-surface-sunken: var(--color-gray-100);
  --color-border: var(--color-gray-200);
  --color-border-strong: var(--color-gray-300);
  --color-text-primary: var(--color-gray-900);
  --color-text-secondary: var(--color-gray-600);
  --color-text-muted: var(--color-gray-500);
  --color-text-on-brand: var(--color-white);
  --color-disabled-bg: var(--color-gray-100);
  --color-disabled-text: var(--color-gray-400);
  --color-hover: rgba(79, 70, 229, 0.07);
  --color-active: rgba(79, 70, 229, 0.13);
  --color-focus: var(--color-primary-500);
  --color-overlay: rgba(15, 23, 42, 0.58);
  --color-selection: var(--color-primary-100);

  /* Typography */
  --font-family-sans: Inter, ui-sans-serif, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji";
  --font-family-display: var(--font-family-sans);
  --font-family-mono: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;

  --font-size-display: clamp(2.25rem, 5vw, 4rem);
  --font-size-hero: clamp(1.875rem, 4vw, 3rem);
  --font-size-h1: clamp(1.625rem, 3vw, 2.25rem);
  --font-size-h2: clamp(1.25rem, 2vw, 1.5rem);
  --font-size-h3: 1.0625rem;
  --font-size-body-lg: 1.0625rem;
  --font-size-body: 1rem;
  --font-size-small: 0.875rem;
  --font-size-caption: 0.75rem;
  --font-size-button: 0.9375rem;

  --font-weight-light: 300;
  --font-weight-regular: 400;
  --font-weight-medium: 500;
  --font-weight-semibold: 600;
  --font-weight-bold: 700;

  --line-height-tight: 1.2;
  --line-height-heading: 1.3;
  --line-height-body: 1.65;
  --line-height-control: 1.25;
  --letter-spacing-tight: -0.025em;
  --letter-spacing-wide: 0.04em;

  /* Spacing scale */
  --space-0: 0;
  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-5: 1.25rem;
  --space-6: 1.5rem;
  --space-8: 2rem;
  --space-10: 2.5rem;
  --space-12: 3rem;
  --space-16: 4rem;
  --space-20: 5rem;
  --space-section: clamp(2rem, 5vw, 4rem);
  --space-container: clamp(1rem, 3vw, 2rem);

  /* Sizing */
  --container-xs: 32rem;
  --container-sm: 40rem;
  --container-md: 48rem;
  --container-lg: 64rem;
  --container-xl: 80rem;
  --container-2xl: 90rem;
  --sidebar-width: 16.5rem;
  --sidebar-collapsed-width: 5rem;
  --header-height: 4.5rem;
  --control-height-sm: 2.25rem;
  --control-height-md: 2.75rem;
  --control-height-lg: 3.25rem;
  --touch-target: 2.75rem;

  /* Borders and radii */
  --border-width: 1px;
  --radius-xs: 0.25rem;
  --radius-sm: 0.5rem;
  --radius-md: 0.75rem;
  --radius-lg: 1rem;
  --radius-xl: 1.5rem;
  --radius-card: var(--radius-lg);
  --radius-pill: 9999px;
  --radius-circle: 50%;

  /* Shadows */
  --shadow-xs: 0 1px 2px rgba(15, 23, 42, 0.05);
  --shadow-sm: 0 2px 6px rgba(15, 23, 42, 0.07);
  --shadow-md: 0 8px 24px rgba(15, 23, 42, 0.09);
  --shadow-lg: 0 18px 45px rgba(15, 23, 42, 0.12);
  --shadow-floating: 0 12px 35px rgba(15, 23, 42, 0.16);
  --shadow-modal: 0 30px 80px rgba(2, 6, 23, 0.28);
  --shadow-focus: 0 0 0 3px rgba(99, 102, 241, 0.28);

  /* Motion */
  --duration-fast: 120ms;
  --duration-normal: 220ms;
  --duration-slow: 380ms;
  --ease-standard: cubic-bezier(0.2, 0, 0, 1);
  --ease-emphasized: cubic-bezier(0.2, 0.8, 0.2, 1);
  --ease-bounce: cubic-bezier(0.34, 1.56, 0.64, 1);

  /* Z-index layers */
  --z-base: 0;
  --z-navigation: 100;
  --z-dropdown: 300;
  --z-sticky: 400;
  --z-modal-backdrop: 700;
  --z-modal: 800;
  --z-toast: 900;
  --z-loading: 1000;
  --z-tooltip: 1100;
}

/* Explicit theme support. System dark mode appears later as an opt-in fallback. */
[data-theme="dark"] {
  --color-background: #0b1020;
  --color-background-subtle: #10182b;
  --color-surface: #131d31;
  --color-surface-raised: #18233a;
  --color-surface-sunken: #0f172a;
  --color-border: #2b3850;
  --color-border-strong: #3a4963;
  --color-text-primary: #f1f5f9;
  --color-text-secondary: #cbd5e1;
  --color-text-muted: #94a3b8;
  --color-disabled-bg: #1e293b;
  --color-disabled-text: #64748b;
  --color-hover: rgba(129, 140, 248, 0.12);
  --color-active: rgba(129, 140, 248, 0.2);
  --color-overlay: rgba(2, 6, 23, 0.76);
  --color-selection: #3730a3;
  --shadow-xs: 0 1px 2px rgba(0, 0, 0, 0.25);
  --shadow-sm: 0 3px 10px rgba(0, 0, 0, 0.25);
  --shadow-md: 0 10px 28px rgba(0, 0, 0, 0.3);
  --shadow-lg: 0 20px 50px rgba(0, 0, 0, 0.36);
}

/* ========================================================================== 
   2. RESET & BASE STYLES
   ========================================================================== */

*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  min-width: 20rem;
  min-height: 100%;
  color-scheme: light;
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
  text-size-adjust: 100%;
}

html[data-theme="dark"] { color-scheme: dark; }

body,
h1,
h2,
h3,
h4,
p,
figure,
blockquote,
dl,
dd {
  margin: 0;
}

ul[role="list"],
ol[role="list"] {
  margin: 0;
  padding: 0;
  list-style: none;
}

body {
  min-height: 100vh;
  min-height: 100dvh;
  margin: 0;
  overflow-x: hidden;
  background: var(--color-background);
  color: var(--color-text-primary);
  font-family: var(--font-family-sans);
  font-size: var(--font-size-body);
  font-weight: var(--font-weight-regular);
  line-height: var(--line-height-body);
  text-rendering: optimizeLegibility;
  -webkit-font-smoothing: antialiased;
}

img,
picture,
svg,
canvas,
video {
  display: block;
  max-width: 100%;
}

img { height: auto; }

button,
input,
textarea,
select {
  margin: 0;
  color: inherit;
  font: inherit;
}

button,
select,
label[for],
input[type="checkbox"],
input[type="radio"] {
  cursor: pointer;
}

button {
  border: 0;
}

button:disabled,
input:disabled,
select:disabled,
textarea:disabled {
  cursor: not-allowed;
}

textarea { resize: vertical; }

input[type="search"] { appearance: none; }

input[type="search"]::-webkit-search-cancel-button { cursor: pointer; }

fieldset {
  min-width: 0;
  margin: 0;
  padding: 0;
  border: 0;
}

legend { padding: 0; }

table {
  width: 100%;
  border-collapse: collapse;
  border-spacing: 0;
}

hr {
  height: 0;
  margin-block: var(--space-6);
  border: 0;
  border-top: var(--border-width) solid var(--color-border);
}

[hidden] { display: none !important; }

::selection {
  background: var(--color-selection);
  color: var(--color-text-primary);
}

:target { scroll-margin-top: calc(var(--header-height) + var(--space-4)); }

/* ========================================================================== 
   3. TYPOGRAPHY
   ========================================================================== */

h1,
h2,
h3,
h4,
h5,
h6 {
  color: var(--color-text-primary);
  font-family: var(--font-family-display);
  font-weight: var(--font-weight-semibold);
  line-height: var(--line-height-heading);
  letter-spacing: var(--letter-spacing-tight);
  text-wrap: balance;
}

h1 { font-size: var(--font-size-h1); }
h2 { font-size: var(--font-size-h2); }
h3 { font-size: var(--font-size-h3); }

p { text-wrap: pretty; }

small,
.caption,
.text-caption {
  color: var(--color-text-muted);
  font-size: var(--font-size-caption);
  line-height: 1.5;
}

strong { font-weight: var(--font-weight-semibold); }

code,
kbd,
samp,
pre {
  font-family: var(--font-family-mono);
}

code {
  padding: 0.15em 0.35em;
  border-radius: var(--radius-xs);
  background: var(--color-surface-sunken);
  color: var(--color-primary-700);
  font-size: 0.88em;
}

pre {
  max-width: 100%;
  margin-block: var(--space-4);
  padding: var(--space-4);
  overflow: auto;
  border: var(--border-width) solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-gray-900);
  color: var(--color-gray-100);
  font-size: var(--font-size-small);
  line-height: 1.65;
}

pre code {
  padding: 0;
  background: transparent;
  color: inherit;
}

a {
  color: var(--color-primary);
  font-weight: var(--font-weight-medium);
  text-decoration-color: transparent;
  text-decoration-thickness: 0.08em;
  text-underline-offset: 0.2em;
  transition: color var(--duration-fast), text-decoration-color var(--duration-fast);
}

a:hover {
  color: var(--color-primary-hover);
  text-decoration-color: currentColor;
}

.display-text,
.hero-title {
  font-size: var(--font-size-display);
  font-weight: var(--font-weight-bold);
  line-height: var(--line-height-tight);
  letter-spacing: -0.04em;
}

.page-title { font-size: var(--font-size-h1); }
.section-title { font-size: var(--font-size-h2); }
.card-title { font-size: var(--font-size-h3); }
.subtitle,
.lead {
  color: var(--color-text-secondary);
  font-size: var(--font-size-body-lg);
}

.hint,
.help-text {
  color: var(--color-text-muted);
  font-size: var(--font-size-small);
}

.text-label {
  font-size: var(--font-size-small);
  font-weight: var(--font-weight-semibold);
  letter-spacing: 0.01em;
}

/* ========================================================================== 
   4. LAYOUT SYSTEM
   ========================================================================== */

.container,
.container-xl,
.container-lg,
.container-md,
.container-sm {
  width: min(100% - (2 * var(--space-container)), var(--container-xl));
  margin-inline: auto;
}
.container-xl { max-width: var(--container-xl); }
.container-lg { max-width: var(--container-lg); }
.container-md { max-width: var(--container-md); }
.container-sm { max-width: var(--container-sm); }

.page-wrapper {
  width: 100%;
  min-height: calc(100vh - var(--header-height));
  padding: var(--space-container);
}

.content-wrapper {
  width: 100%;
  max-width: var(--container-xl);
  margin-inline: auto;
}

.section,
.app-page {
  padding-block: var(--space-8);
}

.grid {
  display: grid;
  gap: var(--space-6);
}
.grid-2 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
.grid-3 { grid-template-columns: repeat(3, minmax(0, 1fr)); }
.grid-4 { grid-template-columns: repeat(4, minmax(0, 1fr)); }
.grid-auto { grid-template-columns: repeat(auto-fit, minmax(min(100%, 15rem), 1fr)); }

.flex-row,
.flex-column {
  display: flex;
  gap: var(--space-4);
}
.flex-row { align-items: center; }
.flex-column { flex-direction: column; }
.flex-wrap { flex-wrap: wrap; }
.flex-1 { flex: 1 1 0%; }

.centered,
.center-content {
  display: grid;
  place-items: center;
}

.sidebar-layout {
  display: grid;
  grid-template-columns: var(--sidebar-width) minmax(0, 1fr);
  min-height: 100vh;
}

.cluster {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-3);
}

.stack { display: flex; flex-direction: column; }
.stack > * + * { margin-block-start: var(--space-4); }
.stack-sm > * + * { margin-block-start: var(--space-2); }
.stack-lg > * + * { margin-block-start: var(--space-8); }

/* Main application shell */
#app {
  min-height: 100vh;
  min-height: 100dvh;
  padding-top: var(--header-height);
}

#app-header {
  position: fixed;
  z-index: var(--z-navigation);
  inset: 0 0 auto 0;
  display: grid;
  grid-template-columns: var(--sidebar-width) 1fr auto;
  align-items: center;
  min-height: var(--header-height);
  padding: var(--space-3) var(--space-5);
  border-bottom: var(--border-width) solid var(--color-border);
  background: color-mix(in srgb, var(--color-surface) 94%, transparent);
  box-shadow: var(--shadow-xs);
  backdrop-filter: blur(14px);
}

#app-header > a:first-child {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  color: var(--color-text-primary);
  text-decoration: none;
}

#app-header > a:first-child img {
  width: 2.5rem;
  height: 2.5rem;
  object-fit: contain;
}

#app-header > a:first-child strong {
  overflow: hidden;
  font-size: 0.95rem;
  letter-spacing: 0.04em;
  text-overflow: ellipsis;
}

#user-summary {
  display: flex;
  justify-self: end;
  align-items: center;
  gap: var(--space-4);
  margin-right: var(--space-4);
  color: var(--color-text-secondary);
  font-size: var(--font-size-small);
}

#user-summary p:not(:first-child) {
  padding: var(--space-1) var(--space-3);
  border: var(--border-width) solid var(--color-primary-100);
  border-radius: var(--radius-pill);
  background: var(--color-primary-soft);
  color: var(--color-primary-700);
}

#app-header > nav {
  display: flex;
  align-items: center;
  gap: var(--space-2);
}

#app-header > nav > a,
#app-header > nav > button {
  position: relative;
  display: grid;
  width: var(--touch-target);
  height: var(--touch-target);
  padding: 0;
  place-items: center;
  border-radius: var(--radius-circle);
  background: transparent;
  color: var(--color-text-secondary);
  text-decoration: none;
}

#app-header > nav > a:hover,
#app-header > nav > button:hover { background: var(--color-hover); color: var(--color-primary); }

#header-avatar {
  width: 2.25rem;
  height: 2.25rem;
  border: 2px solid var(--color-primary-200);
  border-radius: var(--radius-circle);
  object-fit: cover;
}

#notification-count {
  position: absolute;
  top: 0.15rem;
  right: 0.05rem;
  display: grid;
  min-width: 1.1rem;
  height: 1.1rem;
  padding-inline: 0.25rem;
  place-items: center;
  border: 2px solid var(--color-surface);
  border-radius: var(--radius-pill);
  background: var(--color-danger);
  color: var(--color-white);
  font-size: 0.625rem;
  font-weight: var(--font-weight-bold);
  line-height: 1;
}

#primary-navigation {
  position: fixed;
  z-index: calc(var(--z-navigation) - 1);
  inset: var(--header-height) auto 0 0;
  width: var(--sidebar-width);
  padding: var(--space-5) var(--space-3);
  overflow-y: auto;
  border-right: var(--border-width) solid var(--color-border);
  background: var(--color-surface);
}

#primary-navigation ul {
  display: flex;
  margin: 0;
  padding: 0;
  flex-direction: column;
  gap: var(--space-1);
  list-style: none;
}

#primary-navigation a {
  display: flex;
  min-height: var(--touch-target);
  padding: var(--space-2) var(--space-3);
  align-items: center;
  gap: var(--space-3);
  border-radius: var(--radius-md);
  color: var(--color-text-secondary);
  font-size: var(--font-size-small);
  font-weight: var(--font-weight-medium);
  text-decoration: none;
  transition: background var(--duration-fast), color var(--duration-fast), transform var(--duration-fast);
}

#primary-navigation a span { width: 1.5rem; text-align: center; }
#primary-navigation a:hover { background: var(--color-hover); color: var(--color-primary); transform: translateX(2px); }
#primary-navigation a[aria-current="page"],
#primary-navigation a.active {
  background: var(--color-primary-soft);
  color: var(--color-primary-700);
  font-weight: var(--font-weight-semibold);
  box-shadow: inset 3px 0 var(--color-primary);
}

#main-content,
#app-footer {
  margin-left: var(--sidebar-width);
}

#main-content {
  width: calc(100% - var(--sidebar-width));
  max-width: var(--container-2xl);
  min-height: calc(100vh - var(--header-height));
  padding: var(--space-container);
}

.app-page {
  animation: page-in var(--duration-normal) var(--ease-standard) both;
}

.app-page > header:first-child {
  display: flex;
  margin-bottom: var(--space-8);
  align-items: flex-end;
  justify-content: space-between;
  gap: var(--space-4);
}

.app-page > header:first-child p {
  margin-top: var(--space-1);
  color: var(--color-text-secondary);
}

#app-footer {
  padding: var(--space-8) var(--space-container);
  border-top: var(--border-width) solid var(--color-border);
  color: var(--color-text-muted);
  font-size: var(--font-size-small);
  text-align: center;
}

#app-footer p + p { margin-top: var(--space-1); }

.skip-link {
  position: fixed;
  z-index: var(--z-tooltip);
  top: var(--space-2);
  left: var(--space-2);
  padding: var(--space-2) var(--space-4);
  transform: translateY(-150%);
  border-radius: var(--radius-sm);
  background: var(--color-primary);
  color: var(--color-white);
  text-decoration: none;
  transition: transform var(--duration-fast);
}
.skip-link:focus { transform: translateY(0); }

/* ========================================================================== 
   5. REUSABLE COMPONENTS
   ========================================================================== */

/* Buttons */
button,
.button,
[role="button"] {
  display: inline-flex;
  min-height: var(--control-height-md);
  padding: 0.625rem var(--space-4);
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  border: var(--border-width) solid transparent;
  border-radius: var(--radius-md);
  background: var(--color-primary);
  color: var(--color-text-on-brand);
  font-size: var(--font-size-button);
  font-weight: var(--font-weight-semibold);
  line-height: var(--line-height-control);
  text-align: center;
  text-decoration: none;
  white-space: nowrap;
  box-shadow: var(--shadow-xs);
  transition: background var(--duration-fast), border-color var(--duration-fast), color var(--duration-fast), box-shadow var(--duration-fast), transform var(--duration-fast);
}

button:hover:not(:disabled),
.button:hover:not([aria-disabled="true"]) {
  background: var(--color-primary-hover);
  color: var(--color-white);
  text-decoration: none;
  box-shadow: var(--shadow-sm);
  transform: translateY(-1px);
}

button:active:not(:disabled),
.button:active:not([aria-disabled="true"]) {
  background: var(--color-primary-active);
  box-shadow: none;
  transform: translateY(0) scale(0.985);
}

button:disabled,
.button[aria-disabled="true"] {
  border-color: transparent;
  background: var(--color-disabled-bg);
  color: var(--color-disabled-text);
  box-shadow: none;
  pointer-events: none;
}

.button-secondary,
button[type="button"] {
  border-color: var(--color-border-strong);
  background: var(--color-surface);
  color: var(--color-text-primary);
}

.button-secondary:hover:not(:disabled),
button[type="button"]:hover:not(:disabled) {
  border-color: var(--color-primary-300);
  background: var(--color-primary-soft);
  color: var(--color-primary-700);
}

.button-primary,
button[type="submit"] {
  border-color: var(--color-primary);
  background: var(--color-primary);
  color: var(--color-white);
}

.button-outline {
  border-color: var(--color-primary);
  background: transparent;
  color: var(--color-primary);
}

.button-ghost {
  border-color: transparent;
  background: transparent;
  color: var(--color-text-secondary);
  box-shadow: none;
}

.button-danger,
#delete-account-button,
#reset-data-button,
#delete-note-button,
#delete-chat-button {
  border-color: var(--color-danger-100);
  background: var(--color-danger-50);
  color: var(--color-danger-700);
}

.button-danger:hover:not(:disabled),
#delete-account-button:hover,
#reset-data-button:hover,
#delete-note-button:hover,
#delete-chat-button:hover {
  border-color: var(--color-danger);
  background: var(--color-danger);
  color: var(--color-white);
}

.button-success { background: var(--color-success); color: var(--color-white); }
.button-sm { min-height: var(--control-height-sm); padding: var(--space-1) var(--space-3); font-size: var(--font-size-small); }
.button-lg { min-height: var(--control-height-lg); padding-inline: var(--space-6); font-size: var(--font-size-body); }
.button-icon { width: var(--touch-target); padding: 0; border-radius: var(--radius-circle); }
.button-floating {
  position: fixed;
  z-index: var(--z-sticky);
  right: var(--space-6);
  bottom: var(--space-6);
  width: 3.5rem;
  height: 3.5rem;
  padding: 0;
  border-radius: var(--radius-circle);
  box-shadow: var(--shadow-floating);
}

.button-loading,
button.is-loading {
  position: relative;
  cursor: wait;
}

button.is-loading::before {
  width: 1em;
  height: 1em;
  border: 2px solid currentColor;
  border-right-color: transparent;
  border-radius: var(--radius-circle);
  content: "";
  animation: spin 700ms linear infinite;
}

/* Forms */
form {
  --form-gap: var(--space-5);
}

form > p,
.form-group {
  display: flex;
  margin-bottom: var(--form-gap);
  flex-direction: column;
  gap: var(--space-2);
}

label,
legend {
  color: var(--color-text-primary);
  font-size: var(--font-size-small);
  font-weight: var(--font-weight-semibold);
  line-height: 1.4;
}

input:not([type="checkbox"]):not([type="radio"]):not([type="file"]),
textarea,
select {
  width: 100%;
  min-height: var(--control-height-md);
  padding: 0.625rem var(--space-3);
  border: var(--border-width) solid var(--color-border-strong);
  border-radius: var(--radius-md);
  outline: none;
  background: var(--color-surface);
  color: var(--color-text-primary);
  box-shadow: var(--shadow-xs);
  transition: border-color var(--duration-fast), box-shadow var(--duration-fast), background var(--duration-fast);
}

textarea { min-height: 7rem; line-height: 1.55; }
select { padding-right: 2.5rem; }

input::placeholder,
textarea::placeholder { color: var(--color-text-muted); opacity: 0.85; }

input:hover:not(:disabled),
textarea:hover:not(:disabled),
select:hover:not(:disabled) { border-color: var(--color-gray-400); }

input:focus,
textarea:focus,
select:focus {
  border-color: var(--color-focus);
  box-shadow: var(--shadow-focus);
}

input:disabled,
textarea:disabled,
select:disabled {
  border-color: var(--color-border);
  background: var(--color-disabled-bg);
  color: var(--color-disabled-text);
}

input[aria-invalid="true"],
textarea[aria-invalid="true"],
select[aria-invalid="true"],
.input-error {
  border-color: var(--color-danger);
  box-shadow: 0 0 0 3px color-mix(in srgb, var(--color-danger) 16%, transparent);
}

.input-success { border-color: var(--color-success); }

.field-error,
.form-error {
  color: var(--color-danger);
  font-size: var(--font-size-small);
}

.form-error:not(:empty) {
  padding: var(--space-3);
  border: var(--border-width) solid var(--color-danger-100);
  border-radius: var(--radius-sm);
  background: var(--color-danger-50);
}

input[type="checkbox"],
input[type="radio"] {
  width: 1.125rem;
  height: 1.125rem;
  margin: 0;
  accent-color: var(--color-primary);
  vertical-align: -0.2em;
}

label:has(> input[type="checkbox"]),
label:has(> input[type="radio"]) {
  display: inline-flex;
  min-height: 2rem;
  align-items: center;
  gap: var(--space-2);
  font-weight: var(--font-weight-regular);
}

.switch {
  position: relative;
  display: inline-flex;
  width: 2.75rem;
  height: 1.5rem;
  padding: 0.15rem;
  align-items: center;
  border-radius: var(--radius-pill);
  background: var(--color-gray-300);
  transition: background var(--duration-fast);
}
.switch::after {
  width: 1.2rem;
  height: 1.2rem;
  border-radius: var(--radius-circle);
  background: var(--color-white);
  box-shadow: var(--shadow-sm);
  content: "";
  transition: transform var(--duration-fast) var(--ease-standard);
}
input:checked + .switch { background: var(--color-primary); }
input:checked + .switch::after { transform: translateX(1.25rem); }

/* Cards */
.card,
.feature-card,
.dashboard-card,
.progress-card,
.statistics-card,
.quiz-card {
  padding: var(--space-6);
  border: var(--border-width) solid var(--color-border);
  border-radius: var(--radius-card);
  background: var(--color-surface);
  box-shadow: var(--shadow-xs);
  transition: border-color var(--duration-normal), box-shadow var(--duration-normal), transform var(--duration-normal);
}

.card-hover:hover,
.feature-card:hover {
  border-color: var(--color-primary-200);
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
}

.card-selected,
.card[aria-selected="true"] {
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px var(--color-primary-100);
}

.card-loading { position: relative; overflow: hidden; pointer-events: none; }
.card-loading::after {
  position: absolute;
  inset: 0;
  background: linear-gradient(100deg, transparent 20%, rgba(255,255,255,0.55) 45%, transparent 70%);
  content: "";
  animation: shimmer 1.4s infinite;
}

.badge {
  display: inline-flex;
  min-height: 1.5rem;
  padding: var(--space-1) var(--space-2);
  align-items: center;
  gap: var(--space-1);
  border-radius: var(--radius-pill);
  background: var(--color-gray-100);
  color: var(--color-gray-700);
  font-size: var(--font-size-caption);
  font-weight: var(--font-weight-semibold);
  line-height: 1;
}
.badge-primary { background: var(--color-primary-100); color: var(--color-primary-800); }
.badge-success { background: var(--color-success-100); color: var(--color-success-700); }
.badge-warning { background: var(--color-warning-100); color: var(--color-warning-700); }
.badge-danger { background: var(--color-danger-100); color: var(--color-danger-700); }
.badge-info { background: var(--color-info-100); color: var(--color-info-700); }

/* Progress */
progress {
  width: 100%;
  height: 0.65rem;
  overflow: hidden;
  border: 0;
  border-radius: var(--radius-pill);
  background: var(--color-gray-200);
  color: var(--color-primary);
  accent-color: var(--color-primary);
}
progress::-webkit-progress-bar { border-radius: var(--radius-pill); background: var(--color-gray-200); }
progress::-webkit-progress-value { border-radius: var(--radius-pill); background: linear-gradient(90deg, var(--color-primary), var(--color-secondary)); transition: width var(--duration-slow); }
progress::-moz-progress-bar { border-radius: var(--radius-pill); background: linear-gradient(90deg, var(--color-primary), var(--color-secondary)); }

.circular-progress {
  --progress: 0deg;
  display: grid;
  width: 7.5rem;
  aspect-ratio: 1;
  place-items: center;
  border-radius: var(--radius-circle);
  background: conic-gradient(var(--color-primary) var(--progress), var(--color-gray-200) 0);
}
.circular-progress::before {
  display: grid;
  width: 76%;
  aspect-ratio: 1;
  place-items: center;
  border-radius: inherit;
  background: var(--color-surface);
  content: attr(data-label);
  font-size: var(--font-size-h2);
  font-weight: var(--font-weight-bold);
}

/* Tables */
table {
  overflow: hidden;
  border: var(--border-width) solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-surface);
}
caption {
  padding: var(--space-3);
  color: var(--color-text-secondary);
  font-size: var(--font-size-small);
  text-align: left;
}
th,
td {
  padding: var(--space-3) var(--space-4);
  border-bottom: var(--border-width) solid var(--color-border);
  text-align: left;
  vertical-align: top;
}
th { background: var(--color-background-subtle); font-size: var(--font-size-small); font-weight: var(--font-weight-semibold); }
tbody tr:last-child td { border-bottom: 0; }
tbody tr:hover { background: var(--color-hover); }

/* Modal system */
dialog {
  width: min(calc(100% - 2rem), 36rem);
  max-height: min(85vh, 50rem);
  padding: 0;
  overflow: auto;
  border: var(--border-width) solid var(--color-border);
  border-radius: var(--radius-xl);
  background: var(--color-surface);
  color: var(--color-text-primary);
  box-shadow: var(--shadow-modal);
}

dialog[open] { animation: modal-in var(--duration-normal) var(--ease-emphasized) both; }
dialog::backdrop { background: var(--color-overlay); backdrop-filter: blur(3px); animation: fade-in var(--duration-normal) both; }

dialog > form > header,
dialog > form > footer {
  display: flex;
  padding: var(--space-5) var(--space-6);
  align-items: center;
  justify-content: space-between;
  gap: var(--space-3);
}
dialog > form > header { border-bottom: var(--border-width) solid var(--color-border); }
dialog > form > footer { border-top: var(--border-width) solid var(--color-border); }
dialog > form > header button { width: var(--touch-target); padding: 0; border-radius: var(--radius-circle); }
#modal-description,
#modal-content { padding-inline: var(--space-6); }
#modal-description { padding-top: var(--space-5); color: var(--color-text-secondary); }
#modal-content { padding-block: var(--space-5); }
#confirmation-dialog form { padding: var(--space-6); }
#confirmation-dialog h2 { margin-bottom: var(--space-2); }
#confirmation-dialog p { margin-bottom: var(--space-6); color: var(--color-text-secondary); }
#confirmation-dialog button { margin-right: var(--space-2); }
#confirmation-submit-button { background: var(--color-danger); border-color: var(--color-danger); color: var(--color-white); }

/* Toasts */
#toast-container {
  position: fixed;
  z-index: var(--z-toast);
  top: calc(var(--header-height) + var(--space-4));
  right: var(--space-4);
  display: flex;
  width: min(calc(100% - 2rem), 24rem);
  flex-direction: column;
  gap: var(--space-3);
  pointer-events: none;
}
.toast {
  position: relative;
  display: grid;
  grid-template-columns: 1fr auto;
  padding: var(--space-4);
  border: var(--border-width) solid var(--color-border);
  border-left: 4px solid var(--color-info);
  border-radius: var(--radius-md);
  background: var(--color-surface-raised);
  box-shadow: var(--shadow-floating);
  pointer-events: auto;
  animation: toast-in var(--duration-normal) var(--ease-emphasized) both;
}
.toast-title { align-self: center; }
.toast-message { grid-column: 1 / -1; margin-top: var(--space-1); color: var(--color-text-secondary); font-size: var(--font-size-small); }
.toast-close { grid-area: 1 / 2; width: 2rem; min-height: 2rem; padding: 0; border-radius: var(--radius-circle); }
.toast-success { border-left-color: var(--color-success); }
.toast-error { border-left-color: var(--color-danger); }
.toast-warning { border-left-color: var(--color-warning); }
.toast-info { border-left-color: var(--color-info); }
.toast.is-hiding { animation: toast-out var(--duration-normal) both; }

/* Loading and skeletons */
.spinner {
  display: inline-block;
  width: 2rem;
  height: 2rem;
  border: 3px solid var(--color-primary-100);
  border-top-color: var(--color-primary);
  border-radius: var(--radius-circle);
  animation: spin 750ms linear infinite;
}

.skeleton {
  min-height: 1rem;
  overflow: hidden;
  border-radius: var(--radius-sm);
  background: linear-gradient(90deg, var(--color-gray-100) 20%, var(--color-gray-200) 45%, var(--color-gray-100) 70%);
  background-size: 220% 100%;
  color: transparent !important;
  animation: skeleton-wave 1.4s linear infinite;
}

#loading-overlay {
  position: fixed;
  z-index: var(--z-loading);
  inset: 0;
  display: grid;
  padding: var(--space-6);
  place-content: center;
  gap: var(--space-4);
  background: var(--color-overlay);
  color: var(--color-white);
  text-align: center;
  backdrop-filter: blur(4px);
}
#loading-overlay progress { width: min(18rem, 75vw); }

/* Empty state */
.empty-state {
  display: flex;
  min-height: 18rem;
  padding: var(--space-8);
  align-items: center;
  justify-content: center;
  flex-direction: column;
  gap: var(--space-3);
  border: var(--border-width) dashed var(--color-border-strong);
  border-radius: var(--radius-lg);
  background: var(--color-background-subtle);
  text-align: center;
}
.empty-state img { margin-bottom: var(--space-2); opacity: 0.9; }
.empty-state p { max-width: 28rem; color: var(--color-text-secondary); }

/* Global error */
#global-error {
  position: fixed;
  z-index: var(--z-toast);
  right: var(--space-4);
  bottom: var(--space-4);
  width: min(calc(100% - 2rem), 30rem);
  padding: var(--space-5);
  border: var(--border-width) solid var(--color-danger-100);
  border-left: 4px solid var(--color-danger);
  border-radius: var(--radius-lg);
  background: var(--color-surface);
  box-shadow: var(--shadow-floating);
}
#global-error p { margin: var(--space-2) 0 var(--space-4); color: var(--color-text-secondary); }
#global-error button + button { margin-left: var(--space-2); }

/* Notifications panel */
#notifications-panel {
  position: fixed;
  z-index: var(--z-dropdown);
  top: calc(var(--header-height) - var(--space-1));
  right: var(--space-4);
  width: min(calc(100% - 2rem), 24rem);
  max-height: min(75vh, 40rem);
  overflow: auto;
  border: var(--border-width) solid var(--color-border);
  border-radius: var(--radius-lg);
  background: var(--color-surface-raised);
  box-shadow: var(--shadow-floating);
  animation: dropdown-in var(--duration-fast) var(--ease-standard) both;
}
#notifications-panel > header { display: flex; padding: var(--space-4); align-items: center; gap: var(--space-2); border-bottom: var(--border-width) solid var(--color-border); }
#notifications-panel > header h2 { margin-right: auto; font-size: var(--font-size-h3); }
#notifications-panel > header button { min-height: 2rem; padding: var(--space-1) var(--space-2); font-size: var(--font-size-caption); }
#notifications-list { margin: 0; padding: 0; list-style: none; }
#notifications-list li { padding: var(--space-4); border-bottom: var(--border-width) solid var(--color-border); }

/* ========================================================================== 
   6. FEATURE-SPECIFIC STYLES
   ========================================================================== */

/* Loading screen */
#loading-screen {
  position: fixed;
  z-index: var(--z-loading);
  inset: 0;
  display: flex;
  min-height: 100vh;
  padding: var(--space-6);
  align-items: center;
  justify-content: center;
  flex-direction: column;
  background:
    radial-gradient(circle at 50% 35%, rgba(99, 102, 241, 0.13), transparent 35%),
    var(--color-background);
  text-align: center;
}
#loading-screen img { width: 5.5rem; height: 5.5rem; margin-bottom: var(--space-5); object-fit: contain; animation: logo-breathe 1.8s ease-in-out infinite; }
#loading-screen h1 { font-size: clamp(1.5rem, 5vw, 2.25rem); letter-spacing: 0.08em; }
#loading-screen progress { width: min(18rem, 70vw); margin-block: var(--space-6) var(--space-3); }
#loading-status { color: var(--color-text-secondary); font-size: var(--font-size-small); }

/* Authentication */
#authentication {
  display: grid;
  min-height: 100vh;
  min-height: 100dvh;
  padding: var(--space-6);
  place-content: center;
  background:
    radial-gradient(circle at 15% 15%, rgba(6, 182, 212, 0.12), transparent 28%),
    radial-gradient(circle at 85% 80%, rgba(99, 102, 241, 0.14), transparent 32%),
    var(--color-background);
}

#authentication > header {
  margin-bottom: var(--space-6);
  text-align: center;
}
#authentication > header img { margin: 0 auto var(--space-3); }
#authentication > header h1 { font-size: var(--font-size-h2); }
#authentication > header p { margin-top: var(--space-1); color: var(--color-text-secondary); }

#authentication > section {
  width: min(100%, 28rem);
  padding: var(--space-8);
  border: var(--border-width) solid var(--color-border);
  border-radius: var(--radius-xl);
  background: color-mix(in srgb, var(--color-surface) 96%, transparent);
  box-shadow: var(--shadow-lg);
}
#authentication > section h2 { margin-bottom: var(--space-5); text-align: center; }
#authentication form > button { width: 100%; margin-top: var(--space-3); }
#authentication form > button[type="submit"] { margin-top: 0; }
#authentication form > button:not([type="submit"]) { border-color: transparent; background: transparent; color: var(--color-primary); box-shadow: none; }

/* Dashboard */
#dashboard-section {
  display: grid;
  grid-template-columns: repeat(12, minmax(0, 1fr));
  gap: var(--space-6);
}
#dashboard-section > header { grid-column: 1 / -1; }
#dashboard-section > section {
  padding: var(--space-6);
  border: var(--border-width) solid var(--color-border);
  border-radius: var(--radius-card);
  background: var(--color-surface);
  box-shadow: var(--shadow-xs);
}
#dashboard-section > section > h2 { margin-bottom: var(--space-5); font-size: var(--font-size-h3); }
#dashboard-section > section:nth-of-type(1) { grid-column: 1 / -1; display: grid; grid-template-columns: repeat(4, 1fr); gap: var(--space-4); }
#dashboard-section > section:nth-of-type(1) > h2 { grid-column: 1 / -1; }
#dashboard-section > section:nth-of-type(1) article {
  padding: var(--space-5);
  border-radius: var(--radius-md);
  background: linear-gradient(145deg, var(--color-primary-soft), var(--color-surface));
  box-shadow: inset 0 0 0 1px var(--color-primary-100);
}
#dashboard-section > section:nth-of-type(1) article h3 { color: var(--color-text-secondary); font-size: var(--font-size-small); }
#dashboard-section > section:nth-of-type(1) article p { margin-top: var(--space-2); color: var(--color-primary-700); font-size: var(--font-size-h2); font-weight: var(--font-weight-bold); }
#dashboard-section > section:nth-of-type(2) { grid-column: span 5; }
#dashboard-section > section:nth-of-type(2) button { width: 100%; margin-bottom: var(--space-2); justify-content: flex-start; }
#dashboard-section > section:nth-of-type(3) { grid-column: span 7; background: linear-gradient(135deg, var(--color-primary-700), var(--color-primary-500)); color: var(--color-white); }
#dashboard-section > section:nth-of-type(3) h2,
#dashboard-section > section:nth-of-type(3) h3 { color: var(--color-white); }
#dashboard-section > section:nth-of-type(3) p { margin: var(--space-2) 0 var(--space-5); color: var(--color-primary-100); }
#dashboard-section > section:nth-of-type(n+4) { grid-column: span 4; }
#dashboard-section ul { margin: 0 0 var(--space-4); padding: 0; list-style: none; }
#dashboard-section li { padding-block: var(--space-3); border-bottom: var(--border-width) solid var(--color-border); }

/* AI Tutor */
#ai-section {
  display: grid;
  grid-template-columns: minmax(13rem, 17rem) minmax(0, 1fr);
  grid-template-rows: auto 1fr auto auto;
  gap: var(--space-4);
  min-height: calc(100vh - var(--header-height) - (2 * var(--space-container)));
}
#ai-section > header { grid-column: 1 / -1; }
#ai-section > aside:first-of-type {
  grid-row: 2 / 5;
  padding: var(--space-4);
  border: var(--border-width) solid var(--color-border);
  border-radius: var(--radius-lg);
  background: var(--color-surface);
}
#ai-section > aside:first-of-type h2 { margin-bottom: var(--space-3); font-size: var(--font-size-h3); }
#ai-section > aside:first-of-type button,
#ai-section > aside:first-of-type input { width: 100%; margin-bottom: var(--space-3); }
#chat-history-list { margin: var(--space-2) 0 0; padding: 0; list-style: none; }
#chat-history-list li { padding: var(--space-2) var(--space-3); border-radius: var(--radius-sm); color: var(--color-text-secondary); font-size: var(--font-size-small); cursor: pointer; }
#chat-history-list li:hover { background: var(--color-hover); color: var(--color-primary); }

#ai-conversation {
  display: flex;
  min-height: 28rem;
  max-height: 60vh;
  overflow: hidden;
  flex-direction: column;
  border: var(--border-width) solid var(--color-border);
  border-radius: var(--radius-lg);
  background: var(--color-surface);
}
#ai-conversation > header { display: flex; padding: var(--space-3) var(--space-4); align-items: center; gap: var(--space-2); border-bottom: var(--border-width) solid var(--color-border); }
#ai-conversation > header h2 { margin-right: auto; font-size: var(--font-size-h3); }
#ai-conversation > header button { min-height: var(--control-height-sm); padding: var(--space-1) var(--space-2); font-size: var(--font-size-caption); }
#message-list { flex: 1; margin: 0; padding: var(--space-5); overflow-y: auto; list-style: none; scroll-behavior: smooth; }
.chat-message { display: flex; margin-bottom: var(--space-5); }
.chat-message article { max-width: min(85%, 48rem); padding: var(--space-3) var(--space-4); border-radius: var(--radius-lg); background: var(--color-background-subtle); }
.chat-message article header { display: flex; margin-bottom: var(--space-1); align-items: center; gap: var(--space-3); font-size: var(--font-size-caption); }
.chat-message article time { color: var(--color-text-muted); }
.chat-message.user { justify-content: flex-end; }
.chat-message.user article { border-bottom-right-radius: var(--radius-xs); background: var(--color-primary); color: var(--color-white); }
.chat-message.user article strong,
.chat-message.user article time { color: var(--color-primary-100); }
.chat-message.assistant article { border: var(--border-width) solid var(--color-border); border-bottom-left-radius: var(--radius-xs); background: var(--color-surface); }
.chat-message.assistant p + p,
.chat-message.assistant ul,
.chat-message.assistant ol,
.chat-message.assistant table { margin-top: var(--space-3); }
#ai-thinking { margin: 0 var(--space-5) var(--space-4); color: var(--color-primary); font-size: var(--font-size-small); }
#ai-thinking::after { display: inline-block; width: 1.5em; content: "…"; overflow: hidden; vertical-align: bottom; animation: typing-dots 1.2s steps(4, end) infinite; }
#ai-sources { padding: var(--space-4); border-top: var(--border-width) solid var(--color-border); background: var(--color-background-subtle); }
#ai-sources h3 { font-size: var(--font-size-small); }

#ai-section > section { display: flex; flex-wrap: wrap; align-items: center; gap: var(--space-2); }
#ai-section > section h2 { width: 100%; font-size: var(--font-size-small); }
.suggested-prompt { min-height: var(--control-height-sm); border-color: var(--color-primary-200); border-radius: var(--radius-pill); color: var(--color-primary-700); font-size: var(--font-size-small); }
#ai-message-form {
  position: relative;
  display: grid;
  grid-template-columns: auto auto 1fr auto;
  gap: var(--space-2);
  padding: var(--space-3);
  border: var(--border-width) solid var(--color-border);
  border-radius: var(--radius-lg);
  background: var(--color-surface);
  box-shadow: var(--shadow-sm);
}
#ai-message-form label { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0,0,0,0); }
#ai-message-input { grid-column: 1 / -1; min-height: 4.5rem; border: 0; box-shadow: none; }
#send-message-button { grid-column: 4; }

/* Notes */
#notes-toolbar {
  display: grid;
  grid-template-columns: 1fr 13rem 13rem;
  gap: var(--space-3);
  margin-bottom: var(--space-6);
  align-items: end;
}
#notes-toolbar label { align-self: end; }
#notes-toolbar label:first-child { grid-column: 1; }
#notes-toolbar input { grid-column: 1; }
#notes-toolbar label[for="notes-filter"] { grid-area: 1 / 2; }
#notes-filter { grid-area: 2 / 2; }
#notes-toolbar label[for="notes-sort"] { grid-area: 1 / 3; }
#notes-sort { grid-area: 2 / 3; }

#note-drop-zone {
  display: flex;
  min-height: 14rem;
  margin-bottom: var(--space-8);
  padding: var(--space-8);
  align-items: center;
  justify-content: center;
  flex-direction: column;
  border: 2px dashed var(--color-primary-300);
  border-radius: var(--radius-lg);
  background: var(--color-primary-soft);
  text-align: center;
  transition: border-color var(--duration-normal), background var(--duration-normal), transform var(--duration-normal);
}
#note-drop-zone:hover,
#note-drop-zone.is-dragging { border-color: var(--color-primary); background: var(--color-primary-100); transform: scale(1.005); }
#note-drop-zone h2 { font-size: var(--font-size-h3); }
#note-drop-zone p { margin-block: var(--space-1) var(--space-4); color: var(--color-text-secondary); }
#note-drop-zone label { display: inline-flex; padding: var(--space-2) var(--space-4); border-radius: var(--radius-md); background: var(--color-primary); color: var(--color-white); }
#note-file-input { margin-top: var(--space-3); max-width: 100%; font-size: var(--font-size-small); }

#notes-list { display: grid; margin: 0; padding: 0; grid-template-columns: repeat(auto-fill, minmax(15rem, 1fr)); gap: var(--space-4); list-style: none; }
#notes-list article { height: 100%; padding: var(--space-5); border: var(--border-width) solid var(--color-border); border-radius: var(--radius-card); background: var(--color-surface); box-shadow: var(--shadow-xs); }
#notes-list article:hover { border-color: var(--color-primary-200); box-shadow: var(--shadow-md); transform: translateY(-2px); }
#notes-list .note-summary { margin-block: var(--space-2); color: var(--color-text-secondary); font-size: var(--font-size-small); }
#notes-list .note-updated { display: block; margin-bottom: var(--space-4); color: var(--color-text-muted); font-size: var(--font-size-caption); }
#notes-list button { min-height: var(--control-height-sm); padding: var(--space-1) var(--space-2); font-size: var(--font-size-caption); }

#note-preview { position: fixed; z-index: var(--z-dropdown); inset: var(--header-height) 0 0 auto; width: min(100%, 42rem); overflow-y: auto; border-left: var(--border-width) solid var(--color-border); background: var(--color-surface); box-shadow: var(--shadow-floating); animation: slide-left var(--duration-normal) both; }
#note-preview > header { position: sticky; top: 0; display: flex; padding: var(--space-4); align-items: center; gap: var(--space-2); border-bottom: var(--border-width) solid var(--color-border); background: var(--color-surface); }
#note-preview > header h2 { margin-right: auto; }
#note-preview-content { padding: var(--space-8); }

/* Flashcards */
#flashcard-settings-form,
#quiz-settings-form {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: var(--space-3) var(--space-4);
  margin-bottom: var(--space-8);
  padding: var(--space-5);
  border: var(--border-width) solid var(--color-border);
  border-radius: var(--radius-lg);
  background: var(--color-surface);
}
#flashcard-settings-form fieldset { display: flex; grid-column: 1 / -1; gap: var(--space-5); }
#flashcard-settings-form fieldset legend { margin-bottom: var(--space-2); }
#flashcard-settings-form button { justify-self: start; }

#flashcard-study-area { max-width: 50rem; margin-inline: auto; text-align: center; perspective: 1000px; }
#flashcard-study-area > h2 { margin-bottom: var(--space-1); }
#flashcard-study-area > p { margin-bottom: var(--space-4); color: var(--color-text-muted); }
#flashcard-viewer {
  position: relative;
  display: grid;
  min-height: 22rem;
  padding: var(--space-8);
  place-items: center;
  border: var(--border-width) solid var(--color-border);
  border-radius: var(--radius-xl);
  background: linear-gradient(145deg, var(--color-surface), var(--color-primary-soft));
  box-shadow: var(--shadow-lg);
  cursor: pointer;
  transform-style: preserve-3d;
  transition: transform var(--duration-slow) var(--ease-standard), box-shadow var(--duration-normal);
}
#flashcard-viewer:hover { box-shadow: var(--shadow-floating); }
#flashcard-viewer.is-flipped { transform: rotateY(180deg); }
#flashcard-front,
#flashcard-back { width: 100%; backface-visibility: hidden; }
#flashcard-back { transform: rotateY(180deg); }
#flashcard-viewer h3 { margin-bottom: var(--space-4); color: var(--color-primary); font-size: var(--font-size-small); letter-spacing: var(--letter-spacing-wide); text-transform: uppercase; }
#flashcard-viewer p { font-size: clamp(1.2rem, 3vw, 1.75rem); font-weight: var(--font-weight-medium); line-height: 1.5; }
#flashcard-study-area > nav { display: flex; margin-block: var(--space-6); justify-content: center; flex-wrap: wrap; gap: var(--space-2); }
#flashcard-rating-controls { display: flex; padding: var(--space-4); justify-content: center; flex-wrap: wrap; gap: var(--space-2); border: var(--border-width) solid var(--color-border); border-radius: var(--radius-lg); background: var(--color-surface); }
#flashcard-rating-controls legend { width: 100%; margin-bottom: var(--space-2); }
#flashcard-rating-controls [data-rating="again"] { color: var(--color-danger); }
#flashcard-rating-controls [data-rating="hard"] { color: var(--color-warning-700); }
#flashcard-rating-controls [data-rating="good"] { color: var(--color-info); }
#flashcard-rating-controls [data-rating="easy"] { color: var(--color-success); }

/* Quiz */
#quiz-settings-form h2 { grid-column: 1 / -1; margin-bottom: var(--space-2); }
#quiz-settings-form label:has(input[type="checkbox"]),
#quiz-settings-form button { align-self: end; }
#quiz-player,
#quiz-results { max-width: 52rem; margin-inline: auto; }
#quiz-player > header { display: grid; grid-template-columns: 1fr auto; margin-bottom: var(--space-5); gap: var(--space-2); }
#quiz-player > header progress { grid-column: 1; }
#quiz-timer { grid-area: 1 / 2 / 3; align-self: center; padding: var(--space-2) var(--space-3); border-radius: var(--radius-pill); background: var(--color-gray-100); color: var(--color-text-secondary); font-family: var(--font-family-mono); font-weight: var(--font-weight-semibold); }
#quiz-timer.is-warning { background: var(--color-warning-100); color: var(--color-warning-700); animation: timer-pulse 1s infinite; }
#question-card { padding: var(--space-8); border: var(--border-width) solid var(--color-border); border-radius: var(--radius-xl); background: var(--color-surface); box-shadow: var(--shadow-md); }
#question-text { margin-bottom: var(--space-6); font-size: var(--font-size-h2); }
#quiz-options { display: grid; gap: var(--space-3); }
#quiz-options label {
  display: flex;
  min-height: var(--control-height-lg);
  padding: var(--space-3) var(--space-4);
  align-items: center;
  gap: var(--space-3);
  border: var(--border-width) solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-surface);
  font-weight: var(--font-weight-medium);
  transition: border-color var(--duration-fast), background var(--duration-fast), transform var(--duration-fast);
}
#quiz-options label:hover { border-color: var(--color-primary-300); background: var(--color-primary-soft); transform: translateX(2px); }
#quiz-options label.is-selected { border-color: var(--color-primary); background: var(--color-primary-50); }
#quiz-options label.is-correct { border-color: var(--color-success); background: var(--color-success-50); color: var(--color-success-700); }
#quiz-options label.is-incorrect { border-color: var(--color-danger); background: var(--color-danger-50); color: var(--color-danger-700); }
#answer-explanation { margin-block: var(--space-4); padding: var(--space-5); border-left: 4px solid var(--color-info); border-radius: var(--radius-md); background: var(--color-info-50); }
#answer-explanation h3 { color: var(--color-info-700); }
#answer-explanation p { margin-top: var(--space-1); color: var(--color-gray-700); }
#quiz-player > button { margin-top: var(--space-4); margin-right: var(--space-2); }
#quiz-results { padding: var(--space-8); border: var(--border-width) solid var(--color-border); border-radius: var(--radius-xl); background: var(--color-surface); box-shadow: var(--shadow-md); text-align: center; }
#quiz-results > p { margin: var(--space-4) 0; font-size: var(--font-size-h2); }
#quiz-answer-review { margin-block: var(--space-6); text-align: left; }

/* Concept map */
#concept-map-section > nav { display: flex; margin-bottom: var(--space-3); justify-content: flex-end; flex-wrap: wrap; gap: var(--space-2); }
#concept-map-zoom-in,
#concept-map-zoom-out { width: var(--touch-target); padding: 0; font-size: 1.25rem; }
#concept-map-section figure { position: relative; overflow: hidden; border: var(--border-width) solid var(--color-border); border-radius: var(--radius-lg); background: radial-gradient(circle, var(--color-gray-300) 1px, transparent 1px), var(--color-surface); background-size: 20px 20px; box-shadow: var(--shadow-sm); }
#concept-map-canvas { width: 100%; min-height: 34rem; }
#concept-map-description { padding: var(--space-2) var(--space-4); border-top: var(--border-width) solid var(--color-border); background: var(--color-background-subtle); color: var(--color-text-muted); font-size: var(--font-size-caption); }
#concept-map-legend { margin-top: var(--space-4); padding: var(--space-4); border: var(--border-width) solid var(--color-border); border-radius: var(--radius-md); background: var(--color-surface); }
#concept-map-legend h2,
#map-outline-heading { font-size: var(--font-size-h3); }
#legend-items { display: flex; margin: var(--space-2) 0 0; padding: 0; flex-wrap: wrap; gap: var(--space-4); list-style: none; }
#concept-map-section:fullscreen { padding: var(--space-6); overflow: auto; background: var(--color-background); }
.concept-node { border: 2px solid var(--color-primary); border-radius: var(--radius-pill); background: var(--color-surface); box-shadow: var(--shadow-sm); }
.concept-node:hover,
.concept-node.is-selected { background: var(--color-primary-soft); box-shadow: var(--shadow-md); }
.concept-connection { stroke: var(--color-gray-400); stroke-width: 2; }

/* Progress */
#progress-section { display: grid; grid-template-columns: repeat(12, 1fr); gap: var(--space-5); }
#progress-section > header { grid-column: 1 / -1; }
#progress-section > section { padding: var(--space-5); border: var(--border-width) solid var(--color-border); border-radius: var(--radius-card); background: var(--color-surface); box-shadow: var(--shadow-xs); }
#progress-section > section > h2 { margin-bottom: var(--space-4); font-size: var(--font-size-h3); }
#progress-section > section:nth-of-type(1),
#progress-section > section:nth-of-type(2) { grid-column: span 3; }
#progress-section > section:nth-of-type(3) { grid-column: span 6; }
#progress-section > section:nth-of-type(4),
#progress-section > section:nth-of-type(5) { grid-column: span 6; }
#progress-section > section:nth-of-type(n+6) { grid-column: span 4; }
#overall-mastery,
#progress-xp { margin-bottom: var(--space-3); color: var(--color-primary); font-size: var(--font-size-h1); font-weight: var(--font-weight-bold); }
#achievements-list,
#recent-sessions-list,
#weak-topics-list,
#strong-topics-list { margin: 0; padding-left: var(--space-5); }
#achievements-list { display: flex; padding: 0; flex-wrap: wrap; gap: var(--space-3); list-style: none; }
.achievement,
.profile-badge { display: grid; width: 5rem; text-align: center; place-items: center; gap: var(--space-1); font-size: var(--font-size-caption); }
.achievement-icon { display: grid; width: 3.25rem; height: 3.25rem; place-items: center; border-radius: var(--radius-circle); background: var(--color-warning-100); color: var(--color-warning-700); font-size: 1.5rem; }
#study-history-chart,
#performance-chart { min-height: 14rem; border-radius: var(--radius-md); background: linear-gradient(180deg, var(--color-primary-soft), transparent); }
#study-history-table { margin-top: var(--space-4); }
.timeline { position: relative; margin: 0; padding-left: var(--space-6); list-style: none; }
.timeline::before { position: absolute; top: var(--space-2); bottom: var(--space-2); left: 0.45rem; width: 2px; background: var(--color-border); content: ""; }
.timeline li { position: relative; padding-bottom: var(--space-5); }
.timeline li::before { position: absolute; top: 0.4rem; left: calc(-1 * var(--space-6) + 0.1rem); width: 0.75rem; height: 0.75rem; border: 2px solid var(--color-surface); border-radius: var(--radius-circle); background: var(--color-primary); box-shadow: 0 0 0 2px var(--color-primary-200); content: ""; }

/* Profile */
#profile-section { display: grid; grid-template-columns: minmax(16rem, 22rem) 1fr; gap: var(--space-6); }
#profile-section > header { grid-column: 1 / -1; }
#profile-card { grid-row: span 3; padding: var(--space-8); border: var(--border-width) solid var(--color-border); border-radius: var(--radius-xl); background: var(--color-surface); box-shadow: var(--shadow-sm); text-align: center; }
#profile-avatar { width: 8rem; height: 8rem; margin: 0 auto var(--space-4); border: 4px solid var(--color-primary-100); border-radius: var(--radius-circle); object-fit: cover; }
#change-avatar-button { margin-bottom: var(--space-4); }
#profile-card dl { display: grid; margin-top: var(--space-5); grid-template-columns: auto 1fr; gap: var(--space-2); text-align: left; }
#profile-card dt { color: var(--color-text-muted); font-size: var(--font-size-small); }
#profile-card dd { text-align: right; overflow-wrap: anywhere; }
#profile-section > section,
#profile-preferences-form { padding: var(--space-6); border: var(--border-width) solid var(--color-border); border-radius: var(--radius-card); background: var(--color-surface); }
#profile-section > section h2,
#profile-preferences-form h2 { margin-bottom: var(--space-4); font-size: var(--font-size-h3); }
#profile-statistics { display: grid; grid-template-columns: repeat(4, 1fr); gap: var(--space-3); }
#profile-statistics > * { margin: 0; }
#profile-statistics dt { grid-row: 2; color: var(--color-text-muted); font-size: var(--font-size-caption); }
#profile-statistics dd { grid-row: 1; color: var(--color-primary); font-size: var(--font-size-h2); font-weight: var(--font-weight-bold); }
#profile-badges { display: flex; margin: 0; padding: 0; gap: var(--space-4); list-style: none; }
#profile-preferences-form { display: grid; gap: var(--space-3); }
#profile-preferences-form button { justify-self: start; }

/* Settings */
#settings-section { max-width: 58rem; }
#settings-form,
#settings-section > section { margin-bottom: var(--space-5); padding: var(--space-6); border: var(--border-width) solid var(--color-border); border-radius: var(--radius-lg); background: var(--color-surface); }
#settings-form fieldset { display: grid; margin-bottom: var(--space-8); gap: var(--space-3); }
#settings-form legend,
#settings-section > section h2 { width: 100%; margin-bottom: var(--space-3); font-size: var(--font-size-h3); }
#settings-form fieldset:has(input[type="radio"]) { grid-template-columns: repeat(3, 1fr); }
#settings-form fieldset:has(input[type="radio"]) legend { grid-column: 1 / -1; }
#settings-form fieldset:has(input[type="radio"]) label {
  min-height: 5rem;
  padding: var(--space-4);
  border: var(--border-width) solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-background-subtle);
}
#settings-form fieldset:has(input[type="radio"]) label:has(input:checked) { border-color: var(--color-primary); background: var(--color-primary-soft); box-shadow: 0 0 0 2px var(--color-primary-100); }
#settings-section > section button { margin: var(--space-2) var(--space-2) 0 0; }
#settings-section > section:last-of-type { border-color: var(--color-danger-100); }
#danger-zone-heading { color: var(--color-danger); }

/* ========================================================================== 
   7. UTILITIES
   ========================================================================== */

.sr-only,
.visually-hidden {
  position: absolute !important;
  width: 1px !important;
  height: 1px !important;
  padding: 0 !important;
  overflow: hidden !important;
  clip: rect(0, 0, 0, 0) !important;
  white-space: nowrap !important;
  border: 0 !important;
}
.not-sr-only { position: static; width: auto; height: auto; overflow: visible; clip: auto; white-space: normal; }

.d-none { display: none !important; }
.d-block { display: block !important; }
.d-inline { display: inline !important; }
.d-inline-block { display: inline-block !important; }
.d-flex { display: flex !important; }
.d-grid { display: grid !important; }

.items-start { align-items: flex-start !important; }
.items-center { align-items: center !important; }
.items-end { align-items: flex-end !important; }
.justify-start { justify-content: flex-start !important; }
.justify-center { justify-content: center !important; }
.justify-between { justify-content: space-between !important; }
.justify-end { justify-content: flex-end !important; }

.gap-1 { gap: var(--space-1) !important; }
.gap-2 { gap: var(--space-2) !important; }
.gap-3 { gap: var(--space-3) !important; }
.gap-4 { gap: var(--space-4) !important; }
.gap-6 { gap: var(--space-6) !important; }
.gap-8 { gap: var(--space-8) !important; }

.m-0 { margin: 0 !important; }
.mt-1 { margin-top: var(--space-1) !important; }
.mt-2 { margin-top: var(--space-2) !important; }
.mt-4 { margin-top: var(--space-4) !important; }
.mt-6 { margin-top: var(--space-6) !important; }
.mt-8 { margin-top: var(--space-8) !important; }
.mb-2 { margin-bottom: var(--space-2) !important; }
.mb-4 { margin-bottom: var(--space-4) !important; }
.mb-6 { margin-bottom: var(--space-6) !important; }
.mx-auto { margin-inline: auto !important; }

.p-0 { padding: 0 !important; }
.p-2 { padding: var(--space-2) !important; }
.p-4 { padding: var(--space-4) !important; }
.p-6 { padding: var(--space-6) !important; }
.p-8 { padding: var(--space-8) !important; }

.w-full { width: 100% !important; }
.h-full { height: 100% !important; }
.max-w-sm { max-width: var(--container-sm) !important; }
.max-w-md { max-width: var(--container-md) !important; }
.max-w-lg { max-width: var(--container-lg) !important; }

.text-left { text-align: left !important; }
.text-center { text-align: center !important; }
.text-right { text-align: right !important; }
.text-primary { color: var(--color-primary) !important; }
.text-secondary { color: var(--color-text-secondary) !important; }
.text-muted { color: var(--color-text-muted) !important; }
.text-success { color: var(--color-success) !important; }
.text-warning { color: var(--color-warning) !important; }
.text-danger { color: var(--color-danger) !important; }
.text-sm { font-size: var(--font-size-small) !important; }
.text-xs { font-size: var(--font-size-caption) !important; }
.font-medium { font-weight: var(--font-weight-medium) !important; }
.font-semibold { font-weight: var(--font-weight-semibold) !important; }
.font-bold { font-weight: var(--font-weight-bold) !important; }
.truncate { overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }

.rounded { border-radius: var(--radius-md) !important; }
.rounded-lg { border-radius: var(--radius-lg) !important; }
.rounded-full { border-radius: var(--radius-pill) !important; }
.shadow-sm { box-shadow: var(--shadow-sm) !important; }
.shadow-md { box-shadow: var(--shadow-md) !important; }
.border { border: var(--border-width) solid var(--color-border) !important; }
.bg-surface { background: var(--color-surface) !important; }

.overflow-hidden { overflow: hidden !important; }
.overflow-auto { overflow: auto !important; }
.pointer-events-none { pointer-events: none !important; }
.select-none { user-select: none !important; }

/* ========================================================================== 
   8. ANIMATIONS
   ========================================================================== */

@keyframes fade-in {
  from { opacity: 0; }
  to { opacity: 1; }
}

@keyframes page-in {
  from { opacity: 0; transform: translateY(0.4rem); }
  to { opacity: 1; transform: translateY(0); }
}

@keyframes modal-in {
  from { opacity: 0; transform: translateY(1rem) scale(0.97); }
  to { opacity: 1; transform: translateY(0) scale(1); }
}

@keyframes toast-in {
  from { opacity: 0; transform: translateX(1.5rem) scale(0.98); }
  to { opacity: 1; transform: translateX(0) scale(1); }
}

@keyframes toast-out {
  to { opacity: 0; transform: translateX(1rem); }
}

@keyframes dropdown-in {
  from { opacity: 0; transform: translateY(-0.5rem) scale(0.98); }
  to { opacity: 1; transform: translateY(0) scale(1); }
}

@keyframes slide-left {
  from { opacity: 0; transform: translateX(2rem); }
  to { opacity: 1; transform: translateX(0); }
}

@keyframes spin { to { transform: rotate(360deg); } }

@keyframes shimmer {
  from { transform: translateX(-100%); }
  to { transform: translateX(100%); }
}

@keyframes skeleton-wave {
  from { background-position: 100% 0; }
  to { background-position: -100% 0; }
}

@keyframes logo-breathe {
  0%, 100% { transform: scale(1); filter: drop-shadow(0 0 0 transparent); }
  50% { transform: scale(1.04); filter: drop-shadow(0 8px 14px rgba(79, 70, 229, 0.18)); }
}

@keyframes typing-dots {
  from { width: 0; }
  to { width: 1.5em; }
}

@keyframes timer-pulse {
  50% { box-shadow: 0 0 0 4px var(--color-warning-100); }
}

.animate-fade-in { animation: fade-in var(--duration-normal) both; }
.animate-page-in { animation: page-in var(--duration-normal) both; }
.animate-spin { animation: spin 750ms linear infinite; }

/* ========================================================================== 
   9. RESPONSIVE & ACCESSIBILITY RULES
   ========================================================================== */

/* Tablet */
@media (max-width: 64rem) {
  :root { --sidebar-width: 5rem; }

  #app-header { grid-template-columns: var(--sidebar-width) 1fr auto; }
  #app-header > a:first-child strong { display: none; }
  #primary-navigation a { justify-content: center; }
  #primary-navigation a span { width: auto; font-size: 1.15rem; }
  #primary-navigation a { font-size: 0; }
  #primary-navigation a span { font-size: 1.15rem; }

  #dashboard-section > section:nth-of-type(2),
  #dashboard-section > section:nth-of-type(3) { grid-column: span 6; }
  #dashboard-section > section:nth-of-type(n+4) { grid-column: span 6; }

  #progress-section > section:nth-of-type(1),
  #progress-section > section:nth-of-type(2) { grid-column: span 6; }
  #progress-section > section:nth-of-type(3),
  #progress-section > section:nth-of-type(n+4) { grid-column: 1 / -1; }

  #profile-statistics { grid-template-columns: repeat(2, 1fr); }
  #profile-statistics dt,
  #profile-statistics dd { grid-row: auto; }

  #notes-toolbar { grid-template-columns: 1fr 1fr; }
  #notes-toolbar label:first-child,
  #notes-toolbar input { grid-column: 1 / -1; }
  #notes-toolbar label[for="notes-filter"] { grid-area: 3 / 1; }
  #notes-filter { grid-area: 4 / 1; }
  #notes-toolbar label[for="notes-sort"] { grid-area: 3 / 2; }
  #notes-sort { grid-area: 4 / 2; }
}

/* Mobile */
@media (max-width: 48rem) {
  :root {
    --header-height: 4rem;
    --space-container: 1rem;
  }

  #app { padding-top: var(--header-height); padding-bottom: 4.5rem; }
  #app-header { grid-template-columns: auto 1fr auto; padding-inline: var(--space-3); }
  #user-summary { justify-self: center; margin-right: 0; }
  #user-summary p:first-child,
  #user-summary p:nth-child(3) { display: none; }
  #app-header > nav > a[aria-label="Open settings"] { display: none; }

  #primary-navigation {
    position: fixed;
    z-index: var(--z-navigation);
    inset: auto 0 0 0;
    width: 100%;
    height: 4.5rem;
    padding: var(--space-1) var(--space-2) max(var(--space-1), env(safe-area-inset-bottom));
    overflow-x: auto;
    overflow-y: hidden;
    border-top: var(--border-width) solid var(--color-border);
    border-right: 0;
    box-shadow: 0 -4px 18px rgba(15, 23, 42, 0.06);
  }
  #primary-navigation ul { min-width: max-content; height: 100%; flex-direction: row; }
  #primary-navigation li:nth-child(n+6):not(:nth-last-child(-n+2)) { display: none; }
  #primary-navigation a { min-width: 4rem; height: 100%; padding: var(--space-1) var(--space-2); justify-content: center; flex-direction: column; gap: 0; font-size: 0.65rem; }
  #primary-navigation a span { font-size: 1rem; }
  #primary-navigation a[aria-current="page"],
  #primary-navigation a.active { box-shadow: inset 0 3px var(--color-primary); }

  #main-content,
  #app-footer { width: 100%; margin-left: 0; }
  #main-content { min-height: auto; }
  #app-footer { padding-bottom: calc(5.5rem + env(safe-area-inset-bottom)); }

  .app-page > header:first-child { align-items: flex-start; flex-direction: column; }

  .grid-2,
  .grid-3,
  .grid-4 { grid-template-columns: 1fr; }
  .sidebar-layout { grid-template-columns: 1fr; }

  #dashboard-section { display: block; }
  #dashboard-section > header,
  #dashboard-section > section { margin-bottom: var(--space-4); }
  #dashboard-section > section:nth-of-type(1) { grid-template-columns: repeat(2, 1fr); }

  #ai-section { display: block; min-height: auto; }
  #ai-section > aside:first-of-type { margin-bottom: var(--space-4); }
  #chat-history-list { display: none; }
  #ai-conversation { min-height: 26rem; max-height: 58vh; margin-bottom: var(--space-4); }
  .chat-message article { max-width: 92%; }
  #ai-section > section { margin-bottom: var(--space-4); }
  #ai-message-form { grid-template-columns: repeat(3, 1fr); }
  #ai-message-form button { width: 100%; padding-inline: var(--space-2); font-size: var(--font-size-caption); }
  #send-message-button { grid-column: 3; }

  #notes-toolbar { display: flex; flex-direction: column; align-items: stretch; }
  #note-drop-zone { min-height: 12rem; padding: var(--space-5); }
  #note-preview { width: 100%; }
  #note-preview > header { flex-wrap: wrap; }
  #note-preview > header h2 { width: 100%; }
  #note-preview-content { padding: var(--space-5); }

  #flashcard-settings-form,
  #quiz-settings-form { grid-template-columns: 1fr; }
  #flashcard-settings-form fieldset { flex-direction: column; gap: var(--space-2); }
  #flashcard-viewer { min-height: 18rem; padding: var(--space-5); }

  #question-card { padding: var(--space-5); }
  #quiz-player > button { width: 100%; margin-right: 0; }

  #concept-map-canvas { min-height: 25rem; }
  #concept-map-section > nav { justify-content: flex-start; }

  #progress-section { display: block; }
  #progress-section > header,
  #progress-section > section { margin-bottom: var(--space-4); }
  #study-history-table { display: block; overflow-x: auto; }

  #profile-section { display: block; }
  #profile-section > header,
  #profile-section > article,
  #profile-section > section,
  #profile-preferences-form { margin-bottom: var(--space-4); }

  #settings-form fieldset:has(input[type="radio"]) { grid-template-columns: 1fr; }
  #settings-form fieldset:has(input[type="radio"]) legend { grid-column: auto; }

  #toast-container { top: calc(var(--header-height) + var(--space-2)); right: var(--space-2); width: calc(100% - (2 * var(--space-2))); }
  #notifications-panel { top: var(--header-height); right: 0; width: 100%; max-height: calc(100vh - var(--header-height) - 4.5rem); border-radius: 0 0 var(--radius-lg) var(--radius-lg); }

  dialog { width: calc(100% - 1rem); max-height: 90vh; border-radius: var(--radius-lg); }
}

/* Small mobile */
@media (max-width: 30rem) {
  #app-header > nav > a[aria-label="Open profile"] { display: none; }
  #dashboard-section > section:nth-of-type(1) { display: block; }
  #dashboard-section > section:nth-of-type(1) article + article { margin-top: var(--space-3); }
  #profile-statistics { grid-template-columns: 1fr; }
  #flashcard-study-area > nav button { flex: 1 1 40%; }
  #authentication { padding: var(--space-3); }
  #authentication > section { padding: var(--space-5); }
  #global-error { right: var(--space-2); bottom: calc(4.5rem + var(--space-2)); width: calc(100% - (2 * var(--space-2))); }
}

/* Visible, consistent keyboard focus */
:focus { outline: none; }
:focus-visible {
  outline: 3px solid var(--color-focus);
  outline-offset: 3px;
  box-shadow: var(--shadow-focus);
}
input:focus-visible,
textarea:focus-visible,
select:focus-visible { outline: 0; }

/* Touch targets for coarse pointers */
@media (pointer: coarse) {
  button,
  .button,
  input,
  select { min-height: var(--touch-target); }
  a { text-underline-offset: 0.25em; }
}

/* Optional automatic dark mode. Explicit data-theme="light" always wins. */
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --color-background: #0b1020;
    --color-background-subtle: #10182b;
    --color-surface: #131d31;
    --color-surface-raised: #18233a;
    --color-surface-sunken: #0f172a;
    --color-border: #2b3850;
    --color-border-strong: #3a4963;
    --color-text-primary: #f1f5f9;
    --color-text-secondary: #cbd5e1;
    --color-text-muted: #94a3b8;
    --color-disabled-bg: #1e293b;
    --color-disabled-text: #64748b;
    --color-hover: rgba(129, 140, 248, 0.12);
    --color-active: rgba(129, 140, 248, 0.2);
    --color-overlay: rgba(2, 6, 23, 0.76);
    --color-selection: #3730a3;
    --shadow-xs: 0 1px 2px rgba(0, 0, 0, 0.25);
    --shadow-sm: 0 3px 10px rgba(0, 0, 0, 0.25);
    --shadow-md: 0 10px 28px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 20px 50px rgba(0, 0, 0, 0.36);
  }

  :root:not([data-theme="light"]) #answer-explanation,
  :root:not([data-theme="light"]) #quiz-options label.is-correct,
  :root:not([data-theme="light"]) #quiz-options label.is-incorrect {
    color: var(--color-gray-900);
  }
}

/* Respect reduced-motion preferences. */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    scroll-behavior: auto !important;
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}

/* High-contrast support. */
@media (forced-colors: active) {
  button,
  .button,
  input,
  textarea,
  select,
  .card,
  #primary-navigation a[aria-current="page"] { border: 1px solid ButtonText; }
  :focus-visible { outline: 3px solid Highlight; }
  progress { border: 1px solid CanvasText; }
}

/* Print study content cleanly. */
@media print {
  #app-header,
  #primary-navigation,
  #app-footer,
  #toast-container,
  #notifications-panel,
  button { display: none !important; }
  #app { padding: 0; }
  #main-content { width: 100%; max-width: none; margin: 0; padding: 0; }
  .app-page { display: block !important; }
  .app-page[hidden] { display: none !important; }
  body { background: #fff; color: #000; }
  .card,
  article,
  section { box-shadow: none !important; break-inside: avoid; }
}