/* ==========================================================================
   小镇刷题家 — CSS Design System
   Morandi Gentle (莫兰迪温柔风)
   Sections: A) Custom Properties  B) Reset & Base  C) Components  D) Responsive
   ========================================================================== */

/* ==========================================================================
   SECTION A: CSS Custom Properties — 3 Theme Skins
   ========================================================================== */

/* ---- Default Theme: Morandi (莫兰迪) ---- */
:root {
  /* Primary palette — dusty rose / muted mauve */
  --color-primary: #B8A9B4;
  --color-primary-light: #D4C5C7;
  --color-primary-dark: #9B8E97;

  /* Accent palette — warm beige / greige */
  --color-accent: #C5BAB0;
  --color-accent-light: #D9CFC6;

  /* Surfaces & backgrounds */
  --color-bg: #F5F0EB;
  --color-surface: #FFFFFF;

  /* Text hierarchy */
  --color-text: #3D3535;
  --color-text-secondary: #8C7E7E;
  --color-text-muted: #B0A5A5;

  /* Borders & shadows */
  --color-border: #E5DCD5;
  --color-shadow: rgba(160, 140, 130, 0.08);

  /* Semantic colors */
  --color-success: #8FA88F;
  --color-danger: #C4908A;

  /* Tags */
  --color-tag-bg: #F0EAE4;
  --color-tag-text: #8C7E7E;

  /* Gradients */
  --gradient-header: linear-gradient(135deg, #B8A9B4 0%, #C5BAB0 100%);

  /* Typography */
  --font-heading: "PingFang SC", "Microsoft YaHei", "Hiragino Sans GB", sans-serif;
  --font-body: "PingFang SC", "Microsoft YaHei", "Hiragino Sans GB", sans-serif;

  /* Font sizes (1rem = 16px) */
  --font-size-xs: 0.75rem;
  --font-size-sm: 0.8125rem;
  --font-size-base: 1rem;
  --font-size-md: 1.0625rem;
  --font-size-lg: 1.25rem;
  --font-size-xl: 1.5rem;

  /* Font weights */
  --font-weight-normal: 400;
  --font-weight-medium: 500;
  --font-weight-semibold: 600;
  --font-weight-bold: 700;

  /* Line heights */
  --line-height-body: 1.6;
  --line-height-heading: 1.3;

  /* Spacing scale */
  --space-xs: 4px;
  --space-sm: 8px;
  --space-md: 12px;
  --space-lg: 16px;
  --space-xl: 20px;
  --space-2xl: 24px;
  --space-3xl: 32px;

  /* Border radii */
  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 20px;
  --radius-full: 9999px;

  /* Touch & layout */
  --touch-target: 44px;
  --max-width: 480px;

  /* Shadows — elevated */
  --shadow-card: 0 2px 12px var(--color-shadow);
  --shadow-card-hover: 0 4px 20px rgba(160, 140, 130, 0.14);
  --shadow-button: 0 2px 8px rgba(184, 169, 180, 0.25);

  /* Transitions */
  --transition-fast: 150ms ease;
  --transition-normal: 250ms ease;
  --transition-slow: 350ms ease;
}

/* ---- Light Theme: clean & crisp ---- */
[data-theme="light"] {
  --color-bg: #F5F5F5;
  --color-surface: #FFFFFF;
  --color-text: #1A1A1A;
  --color-text-secondary: #6B6B6B;
  --color-text-muted: #A0A0A0;
  --color-border: #E5E5E5;
  --color-shadow: rgba(0, 0, 0, 0.06);
  --color-primary: #6B7D8E;
  --color-primary-light: #E2E8EC;
  --color-primary-dark: #4A5C6C;
  --color-accent: #8A9AA8;
  --color-accent-light: #EDF0F3;
  --color-success: #6B9E6B;
  --color-danger: #C47A7A;
  --color-tag-bg: #EEF0F2;
  --color-tag-text: #6B7B88;
  --gradient-header: linear-gradient(135deg, #6B7D8E 0%, #8A9AA8 100%);
  --shadow-card: 0 1px 4px rgba(0, 0, 0, 0.06);
  --shadow-card-hover: 0 2px 12px rgba(0, 0, 0, 0.1);
  --shadow-button: 0 1px 4px rgba(107, 125, 142, 0.2);
}

/* ---- Dark Theme: clean deep charcoal ---- */
[data-theme="dark"] {
  --color-bg: #111111;
  --color-surface: #1C1C1E;
  --color-text: #EBEBEB;
  --color-text-secondary: #9E9E9E;
  --color-text-muted: #666666;
  --color-border: #2C2C2E;
  --color-shadow: rgba(0, 0, 0, 0.4);
  --color-primary: #7B8FA1;
  --color-primary-light: #3A4450;
  --color-primary-dark: #A0B3C4;
  --color-accent: #8A98A5;
  --color-accent-light: #252528;
  --color-success: #5C8F5C;
  --color-danger: #B87070;
  --color-tag-bg: #252528;
  --color-tag-text: #9E9E9E;
  --gradient-header: linear-gradient(135deg, #1C1C1E 0%, #252528 100%);
  --shadow-card: 0 1px 4px rgba(0, 0, 0, 0.5);
  --shadow-card-hover: 0 2px 12px rgba(0, 0, 0, 0.6);
  --shadow-button: 0 1px 4px rgba(123, 143, 161, 0.2);
}


/* ==========================================================================
   SECTION B: Reset & Base Styles
   ========================================================================== */

*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  font-size: 16px;
  -webkit-text-size-adjust: 100%;
  -webkit-tap-highlight-color: transparent;
  overscroll-behavior: contain;
  scroll-behavior: smooth;
}

/* Eliminate 300ms tap delay on mobile */
a, button, .course-header, .subject-card, .video-capsule, .quick-action,
[onclick], .clickable {
  touch-action: manipulation;
}

body {
  font-family: var(--font-body);
  font-size: var(--font-size-base);
  font-weight: var(--font-weight-normal);
  line-height: var(--line-height-body);
  color: var(--color-text);
  background: var(--color-bg);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  max-width: var(--max-width);
  margin: 0 auto;
  min-height: 100vh;
  min-height: 100dvh;
}

a {
  color: inherit;
  text-decoration: none;
}

button,
input,
textarea,
select {
  font: inherit;
  color: inherit;
  border: none;
  outline: none;
  background: none;
}

button {
  cursor: pointer;
  -webkit-appearance: none;
}

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

ul,
ol {
  list-style: none;
}

:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
  border-radius: 4px;
}

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


/* ==========================================================================
   SECTION C: Components
   ========================================================================== */

/* ---- 1. Header Bar ---- */
.header-bar {
  background: var(--gradient-header);
  color: #FFFFFF;
  padding: var(--space-xl) var(--space-lg);
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.header-bar > div:first-child {
  flex: 1;
  text-align: center;
}

.theme-toggle:hover {
  background: rgba(255,255,255,0.15) !important;
}

.header-bar .brand {
  font-family: var(--font-heading);
  font-size: var(--font-size-xl);
  font-weight: var(--font-weight-bold);
  line-height: var(--line-height-heading);
}

.header-bar .tagline {
  font-size: var(--font-size-xs);
  opacity: 0.85;
  margin-top: var(--space-xs);
}


/* ---- 2. Page Header (sticky top bar) ---- */
.page-header {
  position: sticky;
  top: 0;
  display: flex;
  align-items: center;
  gap: var(--space-md);
  padding: var(--space-lg);
  background: rgba(255, 255, 255, 0.85);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--color-border);
  z-index: 10;
}
[data-theme="dark"] .page-header {
  background: rgba(28, 28, 30, 0.85);
}

.page-header .back-btn {
  width: var(--touch-target);
  height: var(--touch-target);
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-full);
  background: transparent;
  transition: background var(--transition-fast);
  flex-shrink: 0;
}

.page-header .back-btn:hover {
  background: var(--color-bg);
}

.page-header .back-btn:active {
  background: var(--color-border);
}

.page-header .back-btn svg {
  width: 24px;
  height: 24px;
  fill: var(--color-text);
}

.page-header .title {
  flex: 1;
  font-family: var(--font-heading);
  font-weight: var(--font-weight-semibold);
  font-size: var(--font-size-md);
  line-height: var(--line-height-heading);
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}


/* ---- 3. Subject Card ---- */
.subject-card {
  display: flex;
  align-items: center;
  gap: var(--space-md);
  background: var(--color-surface);
  border-radius: var(--radius-md);
  padding: var(--space-md) var(--space-lg);
  min-height: var(--touch-target);
  border-left: 4px solid var(--color-primary);
  box-shadow: var(--shadow-card);
  cursor: pointer;
  transition: box-shadow var(--transition-fast), transform var(--transition-fast);
  -webkit-tap-highlight-color: transparent;
}

.subject-card:active {
  transform: scale(0.98);
}

.subject-card .card-icon {
  width: 48px;
  height: 48px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--color-primary-light);
  border-radius: var(--radius-sm);
  flex-shrink: 0;
}

.subject-card .card-icon svg {
  width: 28px;
  height: 28px;
  fill: var(--color-primary-dark);
}

.subject-card .card-body {
  flex: 1;
  min-width: 0;
}

.subject-card .card-body .card-title {
  font-family: var(--font-heading);
  font-size: var(--font-size-md);
  font-weight: var(--font-weight-semibold);
  line-height: var(--line-height-heading);
}

.subject-card .card-body .card-desc {
  font-size: var(--font-size-xs);
  color: var(--color-text-secondary);
  margin-top: 2px;
}

.subject-card .card-arrow {
  flex-shrink: 0;
  width: 20px;
  height: 20px;
}

.subject-card .card-arrow svg {
  width: 20px;
  height: 20px;
  fill: var(--color-text-muted);
}

/* Trial card: expandable with videos inside */
.trial-card {
  flex-wrap: wrap;
}
.trial-card .card-arrow svg {
  transition: transform var(--transition-fast);
}
.trial-videos {
  width: 100%;
  display: flex;
  flex-direction: column;
  gap: var(--space-sm);
  padding: 0 var(--space-md) var(--space-md) var(--space-md);
}


/* ---- 4. Quick Actions Container ---- */
.quick-actions {
  display: flex;
  gap: var(--space-sm);
}


/* ---- 5. Quick Action Item ---- */
.quick-action {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  flex: 1;
  padding: var(--space-md);
  min-height: var(--touch-target);
  background: var(--color-surface);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-card);
  cursor: pointer;
  transition: transform var(--transition-fast), box-shadow var(--transition-fast);
  -webkit-tap-highlight-color: transparent;
}

.quick-action:active {
  transform: scale(0.97);
}

.quick-action svg {
  width: 24px;
  height: 24px;
  fill: var(--color-primary);
}

.quick-action .quick-action-label {
  font-size: var(--font-size-sm);
  color: var(--color-text-secondary);
  margin-top: var(--space-sm);
}


/* ---- 6. Course Card ---- */
.course-card {
  background: var(--color-surface);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-card);
  overflow: hidden;
  transition: box-shadow var(--transition-normal), transform var(--transition-fast);
  cursor: pointer;
}

.course-card:hover {
  box-shadow: var(--shadow-card-hover);
}

.course-header {
  display: flex;
  align-items: center;
  gap: var(--space-md);
  padding: var(--space-lg);
}

.course-header .course-icon {
  width: 40px;
  height: 40px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--color-primary-light);
  border-radius: var(--radius-sm);
  flex-shrink: 0;
}

.course-header .course-icon svg {
  width: 22px;
  height: 22px;
  fill: var(--color-primary-dark);
}

.course-header .course-info {
  flex: 1;
  min-width: 0;
}

.course-header .course-info .course-title {
  font-family: var(--font-heading);
  font-size: var(--font-size-base);
  font-weight: var(--font-weight-semibold);
  line-height: var(--line-height-heading);
}

.course-header .course-info .course-meta {
  font-size: var(--font-size-xs);
  color: var(--color-text-secondary);
  margin-top: 2px;
}

.course-header .expand-icon {
  flex-shrink: 0;
  width: 24px;
  height: 24px;
  transition: transform var(--transition-normal);
}

.course-header .expand-icon svg {
  width: 24px;
  height: 24px;
  fill: var(--color-text-muted);
}


/* ---- 6b. Group Card (level 2: 理论母题/强化刷题) ---- */
.group-card {
  border-left: 4px solid var(--color-primary) !important;
  border-radius: var(--radius-md);
  overflow: hidden;
}

.group-card .course-header {
  padding: var(--space-md) var(--space-lg);
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
}

.group-card .course-header .course-icon {
  background: var(--color-primary);
  width: 44px;
  height: 44px;
}

.group-card .course-header .course-icon svg {
  fill: #FFFFFF;
}

.group-card .course-header .course-title {
  font-size: var(--font-size-md);
  font-weight: var(--font-weight-bold);
  color: var(--color-text);
}
.group-card .course-header .course-meta {
  font-size: var(--font-size-xs);
  color: var(--color-text-muted);
}

/* Course cards nested inside a group card */
.group-courses > .course-card {
  margin-left: var(--space-xl);
  border-left: 3px solid var(--color-border) !important;
  box-shadow: none;
  border-radius: var(--radius-sm);
  background: var(--color-surface);
}

.group-courses > .course-card:last-child {
  margin-bottom: 0;
}

.group-courses > .course-card .course-header {
  padding: var(--space-sm) var(--space-md);
}

.group-courses > .course-card .course-header .course-icon {
  width: 32px;
  height: 32px;
  background: var(--color-bg);
}

.group-courses > .course-card .course-header .course-icon svg {
  fill: var(--color-primary-dark);
  width: 16px;
  height: 16px;
}

.group-courses > .course-card .course-header .course-title {
  font-size: var(--font-size-sm);
  font-weight: var(--font-weight-medium);
  color: var(--color-text-secondary);
}

.group-courses > .course-card .course-header .expand-icon svg {
  width: 20px;
  height: 20px;
}

.course-card.expanded .course-header .expand-icon {
  transform: rotate(180deg);
}

/* Expand/collapse animation */
@keyframes expandIn {
  from { opacity: 0; transform: translateY(-6px); }
  to   { opacity: 1; transform: translateY(0); }
}
.course-card.expanded > .video-capsules,
.course-card.expanded > .group-courses {
  animation: expandIn 0.25s ease;
}

/* Completion check button */
.check-btn {
  width: 36px;
  height: 36px;
  flex-shrink: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  border: 2px solid var(--color-border);
  border-radius: var(--radius-full);
  background: transparent;
  cursor: pointer;
  transition: all var(--transition-fast);
  margin-right: 4px;
  position: relative;
}
/* Subtle hint dot inside the empty circle */
.check-btn::after {
  content: '';
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--color-border);
  opacity: 0.5;
  transition: all var(--transition-fast);
}
.check-btn:hover {
  border-color: var(--color-success);
  transform: scale(1.1);
}
.check-btn:hover::after {
  background: var(--color-success);
  opacity: 0.7;
}
.check-btn:active {
  transform: scale(0.9);
}
.check-btn.checked {
  background: var(--color-success);
  border-color: var(--color-success);
}
.check-btn.checked::after {
  display: none;
}
.check-btn.checked svg {
  width: 16px;
  height: 16px;
  color: #FFFFFF;
}
.check-btn:not(.checked) svg {
  display: none;
}

/* Done state for course cards */
.course-card.done .course-title {
  opacity: 0.7;
}
.course-card.done .course-icon {
  background: var(--color-success) !important;
}

/* Category progress bar */
.progress-bar-wrap {
  height: 4px;
  background: var(--color-border);
  border-radius: 2px;
  margin-top: 6px;
  overflow: hidden;
}
.progress-bar-fill {
  height: 100%;
  background: var(--color-success);
  border-radius: 2px;
  transition: width 0.3s ease;
}
.progress-text {
  font-size: var(--font-size-xs);
  color: var(--color-text-muted);
  margin-top: 2px;
}

/* Press feedback on course headers */
.course-header:active {
  background: rgba(0, 0, 0, 0.03);
}
[data-theme="dark"] .course-header:active {
  background: rgba(255, 255, 255, 0.04);
}

/* Card press feedback */
.subject-card:active {
  transform: scale(0.98);
  box-shadow: var(--shadow-card);
}
.quick-action:active {
  transform: scale(0.95);
  background: var(--color-bg);
}

/* Video capsule press */
.video-capsule:active {
  background: var(--color-border);
}


/* ---- 7. Tag ---- */
.tag {
  display: inline-block;
  font-size: var(--font-size-xs);
  font-weight: var(--font-weight-medium);
  background: var(--color-tag-bg);
  color: var(--color-tag-text);
  border-radius: var(--radius-full);
  padding: 2px 8px;
  line-height: 1.5;
}

.tag.required {
  background: var(--color-primary-light);
  color: var(--color-primary-dark);
}


/* ---- 8. Video Capsules (container) ---- */
.video-capsules {
  display: none !important;
  flex-direction: column;
  gap: var(--space-sm);
  padding: 0 var(--space-lg) var(--space-lg);
}

.course-card.expanded > .video-capsules {
  display: flex !important;
}

/* Group courses container: hidden by default, shown when parent group card is expanded */
.group-courses {
  display: none !important;
  flex-direction: column;
  gap: var(--space-sm);
  padding: 0 var(--space-md) var(--space-md);
}

.course-card.expanded > .group-courses {
  display: flex !important;
}


/* ---- 9. Video Capsule (item) ---- */
.video-capsule {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-md);
  min-height: var(--touch-target);
  background: var(--color-bg);
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: background var(--transition-fast);
}

.video-capsule:hover {
  background: var(--color-border);
}

.video-capsule .play-icon {
  width: 32px;
  height: 32px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--color-primary);
  border-radius: var(--radius-sm);
  background: var(--color-primary);
  border-radius: var(--radius-full);
  flex-shrink: 0;
}

.video-capsule .play-icon svg {
  width: 14px;
  height: 14px;
  fill: #FFFFFF;
}

.video-capsule .video-label {
  flex: 1;
  font-size: var(--font-size-sm);
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
  min-width: 0;
}

.video-capsule .password-badge {
  font-size: var(--font-size-xs);
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-full);
  padding: 2px 8px;
  color: var(--color-text-secondary);
  white-space: nowrap;
  flex-shrink: 0;
}


/* ---- 10. Form Group ---- */
.form-group {
  margin-bottom: var(--space-lg);
}

.form-group label {
  display: block;
  font-size: var(--font-size-sm);
  font-weight: var(--font-weight-medium);
  color: var(--color-text-secondary);
  margin-bottom: var(--space-sm);
}


/* ---- 11. Form Input ---- */
.form-input {
  width: 100%;
  padding: var(--space-md) var(--space-lg);
  background: var(--color-surface);
  border: 1.5px solid var(--color-border);
  border-radius: var(--radius-md);
  font-size: var(--font-size-base);
  min-height: var(--touch-target);
  transition: border-color var(--transition-fast);
}

.form-input:focus {
  border-color: var(--color-primary);
}

.form-input::placeholder {
  color: var(--color-text-muted);
}


/* ---- 12. Buttons ---- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-sm);
  padding: var(--space-md) var(--space-2xl);
  border-radius: var(--radius-md);
  font-size: var(--font-size-base);
  font-weight: var(--font-weight-semibold);
  min-height: var(--touch-target);
  min-width: var(--touch-target);
  transition: all var(--transition-fast);
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
  user-select: none;
}

.btn:active {
  transform: scale(0.97);
}

.btn-primary {
  background: var(--color-primary);
  color: #FFFFFF;
  box-shadow: var(--shadow-button);
}

.btn-primary:hover {
  background: var(--color-primary-dark);
}

.btn-outline {
  background: transparent;
  border: 1.5px solid var(--color-primary);
  color: var(--color-primary-dark);
}

.btn-outline:hover {
  background: var(--color-primary);
  color: #FFFFFF;
}

.btn-block {
  width: 100%;
}

.btn-sm {
  padding: var(--space-sm) var(--space-lg);
  font-size: 0.8125rem;
  min-height: 36px;
}

.btn-danger {
  background: var(--color-danger);
  color: #FFFFFF;
}

.btn-danger:hover {
  opacity: 0.85;
}


/* ---- 13. Toast ---- */
.toast {
  position: fixed;
  top: var(--space-xl);
  left: 50%;
  transform: translateX(-50%) translateY(-120px);
  background: var(--color-text);
  color: var(--color-surface);
  padding: var(--space-md) var(--space-xl);
  border-radius: var(--radius-full);
  font-size: 0.8125rem;
  font-weight: var(--font-weight-medium);
  z-index: 100;
  z-index: 1000;
  pointer-events: none;
  transition: transform var(--transition-normal);
  white-space: nowrap;
  max-width: calc(100vw - 32px);
  overflow: hidden;
  text-overflow: ellipsis;
}

.toast.show {
  transform: translateX(-50%) translateY(0);
  box-shadow: 0 4px 16px rgba(0, 0, 0, 0.15);
}


/* ---- 14. Page Content ---- */
.page-content {
  padding: var(--space-lg);
}


/* ---- 15. Section Title ---- */
.section-title {
  font-size: var(--font-size-sm);
  font-weight: var(--font-weight-medium);
  color: var(--color-text-secondary);
  margin-bottom: var(--space-md);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}


/* ---- 16. Lock Screen ---- */
.lock-screen {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 100dvh;
  padding: var(--space-3xl) var(--space-xl);
  text-align: center;
}

.lock-screen .logo-area {
  margin-bottom: var(--space-3xl);
}

.lock-screen .logo-area .logo-icon {
  width: 72px;
  height: 72px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--gradient-header);
  border-radius: var(--radius-lg);
  margin: 0 auto;
}

.lock-screen .logo-area .logo-icon svg {
  width: 40px;
  height: 40px;
  fill: #FFFFFF;
}

.lock-screen .logo-area h1 {
  font-family: var(--font-heading);
  font-size: var(--font-size-xl);
  font-weight: var(--font-weight-bold);
  line-height: var(--line-height-heading);
  margin-top: var(--space-lg);
}

.lock-screen .logo-area p {
  font-size: var(--font-size-sm);
  color: var(--color-text-secondary);
  margin-top: var(--space-sm);
}

.lock-screen .divider {
  display: flex;
  align-items: center;
  gap: var(--space-md);
  width: 100%;
  margin: var(--space-xl) 0;
  font-size: var(--font-size-sm);
  color: var(--color-text-muted);
}

.lock-screen .divider::before,
.lock-screen .divider::after {
  content: "";
  flex: 1;
  height: 1px;
  background: var(--color-border);
}


/* ---- 17. Skeleton (loading placeholder) ---- */
@keyframes skeleton-shimmer {
  0% {
    background-position: 200% 0;
  }
  100% {
    background-position: -200% 0;
  }
}

.skeleton {
  background: linear-gradient(
    90deg,
    var(--color-border) 0%,
    var(--color-tag-bg) 40%,
    var(--color-border) 70%
  );
  background-size: 200% 100%;
  animation: skeleton-shimmer 1.5s ease-in-out infinite;
  border-radius: var(--radius-sm);
}

.skeleton-text {
  height: 14px;
  margin-bottom: var(--space-sm);
  border-radius: 4px;
}

.skeleton-title {
  height: 20px;
  width: 60%;
  margin-bottom: var(--space-md);
  border-radius: 4px;
}

.skeleton-card {
  height: 72px;
  border-radius: var(--radius-md);
}


/* ---- 18. Modal Overlay ---- */
.modal-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.3);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 100;
}


/* ---- 19. Modal Sheet ---- */
.modal-sheet {
  background: var(--color-surface);
  border-radius: var(--radius-lg) var(--radius-lg) 0 0;
  padding: var(--space-2xl) var(--space-lg);
  width: 100%;
  max-width: var(--max-width);
  max-height: 80vh;
  overflow-y: auto;
  position: fixed;
  bottom: 0;
  left: 50%;
  transform: translateX(-50%);
}

.modal-sheet h3 {
  font-family: var(--font-heading);
  font-size: var(--font-size-lg);
  line-height: var(--line-height-heading);
  margin-bottom: var(--space-lg);
}

.modal-sheet .modal-actions {
  display: flex;
  gap: var(--space-sm);
  margin-top: var(--space-xl);
}


/* ---- 20. Admin Section ---- */
.admin-section {
  margin-bottom: var(--space-3xl);
}

.admin-section h2 {
  font-family: var(--font-heading);
  font-size: var(--font-size-lg);
  line-height: var(--line-height-heading);
  margin-bottom: var(--space-lg);
}


/* ---- 21. Admin Table ---- */
.admin-table {
  width: 100%;
  border-collapse: collapse;
  font-size: var(--font-size-sm);
}

.admin-table th,
.admin-table td {
  padding: var(--space-sm) var(--space-md);
  text-align: left;
  border-bottom: 1px solid var(--color-border);
}

.admin-table th {
  font-weight: var(--font-weight-semibold);
  color: var(--color-text-secondary);
  font-size: var(--font-size-xs);
}

.admin-table td {
  color: var(--color-text);
}


/* ==========================================================================
   SECTION D: Responsive Breakpoints
   ========================================================================== */

/* ---- Tablet: 640px+ ---- */
@media (min-width: 640px) {
  body {
    max-width: 640px;
  }

  .subject-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: var(--space-md);
  }

  .subject-grid .subject-card {
    border-left: none;
    border-top: 4px solid var(--color-primary);
    flex-direction: column;
    text-align: center;
    padding: var(--space-2xl) var(--space-lg);
  }

  .subject-grid .subject-card .card-arrow {
    display: none;
  }

  .page-content {
    padding: var(--space-2xl);
  }
}

/* ---- Desktop: 1024px+ ---- */
@media (min-width: 1024px) {
  body {
    max-width: 960px;
  }

  .subject-grid {
    grid-template-columns: repeat(4, 1fr);
  }

  .header-bar {
    padding: var(--space-3xl) var(--space-3xl);
    border-radius: 0 0 var(--radius-lg) var(--radius-lg);
  }

  .header-bar .brand {
    font-size: 1.75rem;
  }
}