/* ============================================================
   American English Grammar Encyclopedia — Design System v3
   Claymorphism Style — Educational App
   Updated: 2026-09-27 | Based on ui-ux-pro-max recommendations
   ============================================================ */

/* ============ 1. Design Tokens ============ */
:root {
  /* --- Color Palette (Claymorphism: Playful indigo + energetic orange) --- */
  --color-primary: #4F46E5;
  --color-on-primary: #FFFFFF;
  --color-secondary: #818CF8;
  --color-on-secondary: #0F172A;
  --color-accent: #EA580C;
  --color-on-accent: #000000;
  --color-background: #EEF2FF;
  --color-foreground: #1E1B4B;
  --color-card: #FFFFFF;
  --color-card-foreground: #1E1B4B;
  --color-muted: #EBEEF8;
  --color-muted-foreground: #475569;
  --color-border: #C7D2FE;
  --color-destructive: #DC2626;
  --color-on-destructive: #FFFFFF;
  --color-ring: #4F46E5;

  /* --- Legacy aliases (backward compatibility) --- */
  --brand-50:#eef2ff; --brand-100:#e0e7ff; --brand-200:#c7d2fe; --brand-300:#a5b4fc;
  --brand-400:#818cf8; --brand-500:#6366f1; --brand-600:#4f46e5; --brand-700:#4338ca;
  --brand-800:#3730a3; --brand-900:#312e81; --brand-950:#1e1b4b;
  --accent-50:#fffbeb; --accent-100:#fef3c7; --accent-200:#fde68a; --accent-300:#fcd34d;
  --accent-400:#fbbf24; --accent-500:#f59e0b; --accent-600:#d97706; --accent-700:#b45309; --accent-800:#92400e;
  --accent-soft:var(--accent-50); --accent-contrast:#422006; --accent-soft-text:#92400e;
  --n-0:#fff; --n-25:#fcfcfd; --n-50:#f8fafc; --n-100:#f1f5f9; --n-150:#e9eef5;
  --n-200:#e2e8f0; --n-300:#cbd5e1; --n-400:#94a3b8; --n-500:#64748b;
  --n-600:#475569; --n-700:#334155; --n-800:#1e293b; --n-900:#0f172a; --n-950:#020617;

  --bg-canvas: var(--color-background);
  --bg-surface: var(--color-card);
  --bg-elevated: var(--color-card);
  --bg-inset: var(--color-muted);
  --bg-subtle: var(--n-25);
  --text-1: var(--color-foreground);
  --text-2: var(--color-muted-foreground);
  --text-3: #64748b;
  --text-inverse: var(--color-on-primary);
  --border-subtle: var(--n-100);
  --border-default: var(--color-border);
  --border-strong: var(--n-300);
  --primary: var(--color-primary);
  --primary-hover: var(--brand-700);
  --primary-soft: var(--brand-50);
  --accent: var(--color-accent);

  --success-bg:#ecfdf5; --success-border:#a7f3d0; --success-text:#065f46; --success:#10b981;
  --warning-bg:#fffbeb; --warning-border:#fde68a; --warning-text:#92400e; --warning:#f59e0b;
  --danger-bg:#fef2f2; --danger-border:#fecaca; --danger-text:#991b1b; --danger:#ef4444;
  --info-bg:#eff6ff; --info-border:#bfdbfe; --info-text:#1e40af; --info:#3b82f6;

  --c-concept-bg:var(--success-bg); --c-concept-br:var(--success); --c-concept-tx:var(--success-text);
  --c-pitfall-bg:var(--danger-bg); --c-pitfall-br:var(--danger); --c-pitfall-tx:var(--danger-text);
  --c-note-bg:var(--info-bg); --c-note-br:var(--info); --c-note-tx:var(--info-text);
  --c-advanced-bg:#faf5ff; --c-advanced-br:#a855f7; --c-advanced-tx:#6b21a8;
  --c-practice-bg:var(--warning-bg); --c-practice-br:var(--warning); --c-practice-tx:var(--warning-text);
  --c-analysis-bg:#f0f9ff; --c-analysis-br:#0ea5e9; --c-analysis-tx:#075985;

  --sb-bg:#0b1220; --sb-bg-2:#0f172a; --sb-text:#cbd5e1; --sb-text-mute:#94a3b8;
  --sb-border:rgba(148,163,184,.12); --sb-hover:rgba(148,163,184,.08);
  --sb-active-bg:rgba(99,102,241,.15); --sb-active-br:var(--brand-500);

  /* --- Border Radius (Claymorphism: 16-24px rounded) --- */
  --r-xs: 4px;   --r-sm: 8px;   --r-md: 12px;  --r-lg: 16px;
  --r-xl: 20px;  --r-2xl: 24px; --r-full: 999px;

  /* --- Shadow Depths (Claymorphism: double shadows, soft 3D) --- */
  --shadow-sm: 0 1px 2px rgba(0,0,0,0.05), 0 1px 1px rgba(0,0,0,0.03);
  --shadow-md: 0 4px 8px rgba(0,0,0,0.08), 0 2px 4px rgba(0,0,0,0.04);
  --shadow-lg: 0 12px 24px rgba(0,0,0,0.1), 0 4px 8px rgba(0,0,0,0.05);
  --shadow-xl: 0 20px 40px rgba(0,0,0,0.12), 0 8px 16px rgba(0,0,0,0.06);
  --shadow-inner: inset 0 2px 4px rgba(0,0,0,0.05);
  --sh-focus: 0 0 0 3px rgba(79,70,229,0.3);
  --sh-xs: var(--shadow-sm);
  --sh-sm: var(--shadow-md);
  --sh-md: var(--shadow-lg);
  --sh-lg: var(--shadow-xl);

  /* --- Typography --- */
  /* Headings: Baloo 2 (playful, educational) | Body: Cairo (Arabic-optimized, clean) */
  --font-heading: 'Baloo 2', 'Cairo', system-ui, sans-serif;
  --font-body: 'Cairo', 'Noto Sans Arabic', system-ui, sans-serif;
  --font-mono: 'JetBrains Mono', ui-monospace, 'SFMono-Regular', Menlo, monospace;
  --font-sans: var(--font-body); /* default for body text */

  /* --- Spacing Scale (Claymorphism: generous spacing) --- */
  --space-xs: 4px;   --space-sm: 8px;   --space-md: 16px;  --space-lg: 24px;
  --space-xl: 32px;  --space-2xl: 48px; --space-3xl: 64px; --space-4xl: 96px;

  /* --- Transitions (smooth, 150-300ms) --- */
  --ease: cubic-bezier(.4,0,.2,1);
  --ease-out: cubic-bezier(.16,1,.3,1);
  --ease-spring: cubic-bezier(.34,1.56,.64,1);
  --dur-1: 120ms;
  --dur-2: 200ms;
  --dur-3: 320ms;
  --dur-4: 500ms;

  /* --- Layout --- */
  --header-h: 72px;
  --sidebar-w: clamp(240px, 25vw, 320px);
  --toc-w: clamp(180px, 20vw, 260px);
  --content-max: clamp(500px, 70vw, 900px);

  /* --- Compatibility aliases --- */
  --bg: var(--bg-canvas); --bg-alt: var(--bg-surface); --text: var(--text-1); --text-muted: var(--text-2); --text-soft: var(--text-3);
  --primary-dark: var(--primary-hover); --border: var(--border-default); --sidebar-bg: var(--sb-bg); --sidebar-text: var(--sb-text);
  --sidebar-hover: var(--sb-hover); --sidebar-active-bg: var(--sb-active-bg); --sidebar-active-text: #fff;
  --concept-bg: var(--c-concept-bg); --concept-border: var(--c-concept-br); --concept-text: var(--c-concept-tx);
  --pitfall-bg: var(--c-pitfall-bg); --pitfall-border: var(--c-pitfall-br); --pitfall-text: var(--c-pitfall-tx);
  --note-bg: var(--c-note-bg); --note-border: var(--c-note-br); --note-text: var(--c-note-tx);
  --advanced-bg: var(--c-advanced-bg); --advanced-border: var(--c-advanced-br); --advanced-text: var(--c-advanced-tx);
  --practice-bg: var(--c-practice-bg); --practice-border: var(--c-practice-br); --practice-text: var(--c-practice-tx);
  --analysis-bg: var(--c-analysis-bg); --analysis-border: var(--c-analysis-br); --analysis-text: var(--c-analysis-tx);
  --radius: var(--r-lg); --radius-lg: var(--r-xl); --shadow-sm: var(--sh-xs); --shadow: var(--sh-sm); --shadow-lg: var(--sh-lg);
  --font-ar: var(--font-body); --font-en: var(--font-body); --font-code: var(--font-mono); --transition: var(--dur-2) var(--ease);
}

/* ============ Dark Mode (Claymorphism: conditional - requires contrast fixes) ============ */
[data-theme="dark"] {
  --color-background: #0F172A;
  --color-foreground: #E0E7FF;
  --color-card: #1E1B4B;
  --color-card-foreground: #E0E7FF;
  --color-muted: #1E1B4B;
  --color-muted-foreground: #A5B4FC;
  --color-border: #3730A3;
  --color-ring: #818CF8;

  --bg-canvas: var(--color-background);
  --bg-surface: var(--color-card);
  --bg-elevated: #2A2563;
  --bg-inset: var(--color-muted);
  --bg-subtle: #0A1430;
  --text-1: var(--color-foreground);
  --text-2: var(--color-muted-foreground);
  --text-3: #94A3B8;
  --text-inverse: #0F172A;
  --border-subtle: #1E1B4B;
  --border-default: var(--color-border);
  --border-strong: #4338CA;
  --primary: #818CF8;
  --primary-hover: #A5B4FC;
  --primary-soft: #1E1B4B;
  --accent: #F97316;
  --accent-soft: #422006;
  --accent-soft-text: #FDE68A;

  --success-bg: #064E3B; --success-border: #0F766E; --success-text: #A7F3D0;
  --warning-bg: #451A03; --warning-border: #A16207; --warning-text: #FDE68A;
  --danger-bg: #4C0519; --danger-border: #B91C1C; --danger-text: #FECACA;
  --info-bg: #082F49; --info-border: #0369A1; --info-text: #BAE6FD;

  --c-advanced-bg: #2B0F4A; --c-advanced-tx: #E9D5FF;
  --c-analysis-bg: #052E42; --c-analysis-tx: #BAE6FD;

  --sb-bg: #05080F; --sb-bg-2: #0B1220;
}

/* ============ 2. Reset & Global Behavior ============ */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html {
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--header-h) + var(--space-lg));
  -webkit-text-size-adjust: 100%;
  overscroll-behavior-y: none;
  overflow-x: hidden;
}

body {
  font-family: var(--font-body);
  font-size: 16px;
  line-height: 1.8;
  color: var(--text-1);
  background: var(--bg-canvas);
  font-feature-settings: "kern" 1, "liga" 1, "calt" 1;
  text-rendering: optimizeLegibility;
  transition: background var(--dur-2) var(--ease), color var(--dur-2) var(--ease);
  display: flex;
  flex-direction: column;
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* Arabic RTL specific line-height adjustments */
:lang(ar), [dir="rtl"] {
  line-height: 1.9;
  font-feature-settings: "kern" 1, "liga" 1, "calt" 1, "cv02" 1, "cv03" 1;
}

a {
  color: var(--primary);
  text-decoration: none;
  transition: color var(--dur-1) var(--ease);
}
a:hover { color: var(--primary-hover); text-decoration: underline; text-underline-offset: 3px; }

button, input, select, textarea { font-family: inherit; }
button { color: inherit; cursor: pointer; }

/* Accessible focus states */
:focus-visible {
  outline: 3px solid var(--color-ring);
  outline-offset: 3px;
}

/* Selection colors */
::selection { background: var(--brand-200); color: #1E1B4B; }
[data-theme="dark"] ::selection { background: rgba(129,140,248,0.4); color: #fff; }

/* Scrollbar styling */
::-webkit-scrollbar { width: 10px; height: 10px; }
::-webkit-scrollbar-thumb { background: var(--border-strong); border-radius: var(--r-full); border: 2px solid transparent; background-clip: padding-box; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb:hover { background: var(--n-400); }
[data-theme="dark"] ::-webkit-scrollbar-thumb { background: #3730A3; }

/* ============ 3. Site Shell & Header ============ */
.app-header {
  height: var(--header-h);
  padding: 0 var(--space-lg);
  gap: var(--space-md);
  background: color-mix(in srgb, var(--bg-surface) 95%, transparent);
  backdrop-filter: saturate(180%) blur(16px);
  -webkit-backdrop-filter: saturate(180%) blur(16px);
  border-bottom: 1px solid var(--border-subtle);
  box-shadow: var(--shadow-sm);
  display: flex;
  align-items: center;
  justify-content: space-between;
  position: sticky;
  top: 0;
  z-index: 100;
  flex-wrap: wrap;
}

.menu-toggle {
  display: flex;
  width: 48px;
  height: 48px;
  border-radius: var(--r-md);
  align-items: center;
  justify-content: center;
  background: transparent;
  border: 1px solid var(--border-default);
  color: var(--text-1);
  transition: all var(--dur-2) var(--ease);
}
.menu-toggle:hover { background: var(--bg-inset); border-color: var(--brand-300); }
.menu-toggle:focus-visible { outline: 3px solid var(--color-ring); outline-offset: 2px; }

/* Toggle button for sidebar collapse (desktop) */
.sidebar-collapse-btn {
  display: none;
  width: 36px;
  height: 36px;
  border-radius: var(--r-md);
  align-items: center;
  justify-content: center;
  background: var(--bg-inset);
  border: 1px solid var(--border-default);
  color: var(--text-2);
  transition: all var(--dur-2) var(--ease);
  margin-top: var(--space-sm);
}
.sidebar-collapse-btn:hover { background: var(--primary-soft); border-color: var(--primary); color: var(--primary); }
.sidebar-collapse-btn:focus-visible { outline: 3px solid var(--color-ring); outline-offset: 2px; }

/* Collapsed sidebar toggle button visibility */
.layout.sidebar-collapsed .sidebar-collapse-btn { display: flex; }
.layout.sidebar-collapsed .collapse-icon { display: none; }
.layout.sidebar-collapsed .expand-icon { display: block; }

.logo {
  display: flex;
  align-items: center;
  gap: var(--space-md);
  flex-shrink: 0;
  color: var(--text-1);
  text-decoration: none;
}
.logo:hover { text-decoration: none; }

.logo-mark {
  width: 44px;
  height: 44px;
  border-radius: var(--r-lg);
  background: linear-gradient(135deg, var(--brand-600), var(--brand-800));
  box-shadow: var(--shadow-md), inset 0 1px 0 rgba(255,255,255,0.2);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 800;
  font-size: 16px;
  color: white;
  letter-spacing: -0.02em;
}

.logo-text {
  display: flex;
  flex-direction: column;
  gap: 2px;
  line-height: 1.2;
}

.brand-name {
  font-family: var(--font-heading);
  font-weight: 800;
  font-size: 18px;
  color: var(--text-1);
  letter-spacing: -0.02em;
}

.site-title {
  font-family: var(--font-body);
  font-size: 12px;
  color: var(--text-3);
  font-weight: 400;
  letter-spacing: 0.02em;
}

/* Mobile search button */
.m-search-btn {
  display: none;
  width: 44px;
  height: 44px;
  border-radius: var(--r-md);
  align-items: center;
  justify-content: center;
  background: transparent;
  border: 1px solid var(--border-default);
  color: var(--text-2);
  transition: all var(--dur-2) var(--ease);
}
.m-search-btn:hover { background: var(--bg-inset); color: var(--text-1); }

.search-wrap {
  max-width: 560px;
  margin-inline: auto;
  flex: 1;
  display: flex;
  position: relative;
}
.search-wrap input {
  width: 100%;
  height: 48px;
  padding: 0 var(--space-lg);
  padding-inline-end: 52px;
  border-radius: var(--r-lg);
  background: var(--bg-inset);
  border: 2px solid var(--border-default);
  color: var(--text-1);
  font-size: 15px;
  transition: all var(--dur-2) var(--ease);
}
.search-wrap input::placeholder { color: var(--text-3); }
.search-wrap input:focus {
  border-color: var(--primary);
  box-shadow: var(--sh-focus);
  background: var(--bg-surface);
  outline: none;
}
.search-results {
  position: absolute;
  top: calc(100% + 8px);
  inset-inline: 0;
  border-radius: var(--r-lg);
  padding: var(--space-sm);
  background: var(--bg-surface);
  border: 1px solid var(--border-default);
  box-shadow: var(--shadow-xl);
  z-index: 200;
  max-height: 60vh;
  overflow-y: auto;
}
.search-result-item {
  display: block;
  padding: var(--space-sm) var(--space-md);
  border-radius: var(--r-md);
  color: var(--text-1);
  text-decoration: none;
  transition: all var(--dur-1) var(--ease);
}
.search-result-item:hover { background: var(--primary-soft); color: var(--primary); text-decoration: none; }
.search-result-item .sr-title { font-weight: 600; }
.search-result-item .sr-meta { font-size: 12px; color: var(--text-3); margin-top: 2px; }

.header-actions { display: flex; gap: var(--space-sm); align-items: center; }

.icon-btn {
  width: 44px;
  height: 44px;
  border-radius: var(--r-md);
  background: var(--bg-surface);
  border: 1px solid var(--border-default);
  color: var(--text-2);
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--dur-2) var(--ease);
}
.icon-btn:hover {
  background: var(--primary-soft);
  border-color: var(--brand-200);
  color: var(--primary);
  box-shadow: var(--shadow-sm);
  transform: translateY(-1px);
}
.icon-btn:active { transform: translateY(0) scale(0.98); }

/* Reading progress bar */
.reading-progress {
  position: fixed;
  inset-inline: 0;
  top: var(--header-h);
  height: 3px;
  z-index: 98;
  pointer-events: none;
  opacity: 0;
  transition: opacity var(--dur-2);
  background: transparent;
}
.reading-progress.visible { opacity: 1; }
.reading-progress span {
  display: block;
  width: 0;
  height: 100%;
  background: linear-gradient(90deg, var(--accent), var(--primary));
  transition: width 80ms linear;
  border-radius: 0 var(--r-full) var(--r-full) 0;
}

/* Main layout */
.layout {
  display: grid;
  grid-template-columns: var(--sidebar-w) minmax(0, 1fr);
  max-width: 1600px;
  margin-inline: auto;
  flex: 1;
  min-height: 0;
  width: 100%;
  transition: grid-template-columns var(--dur-3) var(--ease-out);
}

/* Sidebar collapsed state on desktop */
.layout.sidebar-collapsed {
  grid-template-columns: 64px minmax(0, 1fr);
}

/* ============ 4. Sidebar (Claymorphism: elevated, soft shadows) ============ */
#sidebar {
  position: sticky;
  top: var(--header-h);
  width: var(--sidebar-w);
  height: calc(100vh - var(--header-h));
  overflow-y: auto;
  padding: var(--space-lg) var(--space-md) var(--space-2xl);
  background: linear-gradient(180deg, var(--sb-bg), var(--sb-bg-2));
  border-inline-end: 1px solid var(--sb-border);
  color: var(--sb-text);
  transition: transform var(--dur-3) var(--ease-out), width var(--dur-3) var(--ease-out);
  scrollbar-width: thin;
  scrollbar-color: var(--border-strong) transparent;
}

/* Collapsed sidebar styles (desktop) */
.layout.sidebar-collapsed #sidebar {
  width: 64px;
  padding-inline: var(--space-sm);
}

.layout.sidebar-collapsed .nav-home span:not(.logo-mark),
.layout.sidebar-collapsed .nav-phase-title,
.layout.sidebar-collapsed .nav-list a span,
.layout.sidebar-collapsed .phase-badge,
.layout.sidebar-collapsed .ch-dot,
.layout.sidebar-collapsed .sidebar-footer {
  display: none !important;
}

.layout.sidebar-collapsed .nav-home {
  justify-content: center;
  padding: var(--space-md);
}

.layout.sidebar-collapsed .nav-list a {
  justify-content: center;
  padding: var(--space-md);
  padding-inline-start: 0;
}

.layout.sidebar-collapsed .nav-list a.active::before,
.layout.sidebar-collapsed .nav-home.active::before {
  display: none;
}

#sidebar::-webkit-scrollbar { width: 8px; }
#sidebar::-webkit-scrollbar-thumb { background: var(--border-strong); border-radius: var(--r-full); border: 2px solid transparent; background-clip: padding-box; }
#sidebar::-webkit-scrollbar-thumb:hover { background: var(--n-400); }

.nav-home {
  display: flex;
  align-items: center;
  gap: var(--space-md);
  padding: var(--space-md) var(--space-lg);
  margin: 0 0 var(--space-sm);
  border-inline-start: 3px solid transparent;
  border-radius: var(--r-lg);
  font-size: 15px;
  font-weight: 600;
  color: var(--sb-text);
  text-decoration: none;
  transition: all var(--dur-2) var(--ease);
}
.nav-home:hover {
  background: var(--sb-hover);
  color: #fff;
  text-decoration: none;
  transform: translateX(-4px);
}
.nav-home.active {
  background: var(--sb-active-bg);
  border-inline-start-color: var(--sb-active-br);
  color: #fff;
}

.nav-phase { margin-top: var(--space-lg); }
.nav-phase-title {
  display: flex;
  align-items: center;
  justify-content: space-between;
  width: 100%;
  padding: var(--space-sm) var(--space-lg);
  border: none;
  background: none;
  border-radius: var(--r-md);
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.05em;
  text-transform: uppercase;
  color: var(--sb-text-mute);
  cursor: pointer;
  text-align: start;
}
.nav-phase-title:hover { background: var(--sb-hover); }
.phase-left { display: flex; align-items: center; gap: var(--space-sm); min-width: 0; }
.phase-left > span:last-child { overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.phase-badge {
  background: rgba(148,163,184,.15);
  color: var(--sb-text-mute);
  border-radius: var(--r-full);
  padding: 2px 8px;
  font-size: 11px;
  font-weight: 600;
}

.nav-list { list-style: none; }
.nav-list a {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-sm) var(--space-lg);
  padding-inline-start: 40px;
  margin: 2px 0;
  border-radius: var(--r-md);
  border-inline-start: 3px solid transparent;
  color: var(--sb-text-mute);
  font-size: 14px;
  font-weight: 500;
  text-decoration: none;
  transition: all var(--dur-2) var(--ease);
}
.nav-list a:hover {
  background: var(--sb-hover);
  color: #fff;
  text-decoration: none;
  transform: translateX(-4px);
}
.nav-list a.active {
  background: var(--sb-active-bg);
  border-inline-start-color: var(--sb-active-br);
  color: #fff;
}
.nav-list a.active .ch-dot { background: var(--brand-400); box-shadow: 0 0 0 3px rgba(99,102,241,.22); }
.nav-list a.done .ch-dot { background: var(--success); }
.ch-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--sb-border);
  flex-shrink: 0;
  transition: all var(--dur-2) var(--ease);
}

/* ============ 5. Reading Canvas, Chapter Title & Side TOC ============ */
#main {
  width: 100%;
  max-width: calc(var(--content-max) + var(--toc-w) + var(--space-3xl));
  margin-inline: auto;
  padding: var(--space-2xl) var(--space-xl) var(--space-4xl);
  min-width: 0;
}

.chapter {
  animation: fadeUp var(--dur-3) var(--ease-out);
}

@keyframes fadeUp {
  from { opacity: 0; transform: translateY(12px); }
  to { opacity: 1; transform: none; }
}

@keyframes popIn {
  from { opacity: 0; transform: translateY(-6px) scale(.98); }
  to { opacity: 1; transform: none; }
}

.chapter-header {
  position: relative;
  padding: var(--space-2xl) var(--space-xl);
  margin-bottom: var(--space-lg);
  border: 1px solid rgba(255,255,255,.14);
  border-radius: var(--r-2xl);
  background: radial-gradient(120% 100% at 100% 0%, rgba(251,191,36,.22), transparent 55%),
              linear-gradient(135deg, var(--brand-700), var(--brand-600) 48%, var(--brand-800));
  color: #fff;
  overflow: hidden;
  box-shadow: var(--shadow-xl), 0 8px 16px -8px rgba(217,119,6,.18);
}

.chapter-header::before {
  content: "";
  position: absolute;
  top: -40%;
  inset-inline-end: -15%;
  width: 420px;
  height: 420px;
  border-radius: 50%;
  background: radial-gradient(circle, rgba(255,255,255,.14), transparent 70%);
  pointer-events: none;
}

.chapter-header::after {
  content: "";
  position: absolute;
  inset: 0;
  background-image:
    linear-gradient(rgba(255,255,255,.035) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255,255,255,.035) 1px, transparent 1px);
  background-size: 40px 40px;
  mask-image: radial-gradient(circle at 100% 0%, #000, transparent 70%);
  pointer-events: none;
}

.phase-label {
  position: relative;
  display: inline-flex;
  align-items: center;
  padding: 6px 14px;
  border-radius: var(--r-full);
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.04em;
  color: #fff;
  background: rgba(255,255,255,.15);
  border: 1px solid rgba(255,255,255,.18);
  margin-bottom: var(--space-md);
}

.chapter-header h1 {
  position: relative;
  font-family: var(--font-heading);
  font-size: clamp(28px, 3.5vw, 42px);
  font-weight: 800;
  line-height: 1.3;
  letter-spacing: -0.02em;
  margin: var(--space-sm) 0 var(--space-md);
  text-shadow: 0 2px 12px rgba(0,0,0,.1);
}

.chapter-header p {
  position: relative;
  color: rgba(255,255,255,.91);
  font-size: 16px;
  line-height: 1.8;
  max-width: 65ch;
}

.chapter-meta {
  position: relative;
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  margin-top: var(--space-lg);
  color: rgba(255,255,255,.78);
  font-size: 13px;
  font-weight: 550;
}

.chapter-layout {
  display: grid;
  grid-template-columns: minmax(0, var(--content-max)) minmax(190px, var(--toc-w));
  justify-content: center;
  align-items: start;
  gap: var(--space-2xl);
  direction: rtl;
}

.chapter-body {
  min-width: 0;
  padding: var(--space-2xl);
  background: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  border-radius: var(--r-xl);
  box-shadow: var(--shadow-sm), var(--shadow-inner);
  overflow-wrap: anywhere;
  overflow: hidden;
  transition: box-shadow var(--dur-3) var(--ease);
}

.chapter-body:hover {
  box-shadow: var(--shadow-md), var(--shadow-inner);
}

.chapter-body > :first-child { margin-top: 0; }
.chapter-body > :last-child { margin-bottom: 0; }

.chapter-toc {
  position: sticky;
  top: calc(var(--header-h) + var(--space-lg));
  max-height: calc(100vh - var(--header-h) - var(--space-2xl));
  overflow: auto;
  padding: var(--space-md) 0 var(--space-lg);
  border-inline-start: 1px solid var(--border-default);
  font-size: 13px;
  scrollbar-width: thin;
  scrollbar-color: var(--border-strong) transparent;
}

.chapter-toc[hidden] { display: none !important; }

.toc-title {
  padding: var(--space-xs) var(--space-lg) var(--space-sm);
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.07em;
  color: var(--text-3);
  text-transform: uppercase;
}

.chapter-toc ol { list-style: none; margin: 0; padding: 0; }
.chapter-toc li { margin: 3px 0; }

.chapter-toc button {
  display: block;
  width: 100%;
  padding: var(--space-sm) var(--space-md);
  border: 0;
  border-inline-start: 2px solid transparent;
  border-radius: 0 var(--r-sm) var(--r-sm) 0;
  background: transparent;
  text-align: start;
  color: var(--text-2);
  font: inherit;
  font-size: 13px;
  line-height: 1.6;
  cursor: pointer;
  transition: all var(--dur-2) var(--ease);
}

[dir="rtl"] .chapter-toc button { border-radius: var(--r-sm) 0 0 var(--r-sm); }

.chapter-toc button:hover {
  background: var(--bg-inset);
  color: var(--primary);
  border-inline-start-color: var(--primary);
}

.chapter-toc button.active {
  background: var(--primary-soft);
  border-inline-start-color: var(--primary);
  color: var(--primary);
  font-weight: 650;
}

.chapter-toc .toc-h3 button {
  padding-inline-start: 28px;
  font-size: 12.5px;
}

.chapter-body h2,
.chapter-body h3 {
  scroll-margin-top: calc(var(--header-h) + var(--space-lg));
}

/* ============ 6. Course Typography & Callouts (Claymorphism: readable, friendly) ============ */
.chapter h2 {
  position: relative;
  margin: var(--space-3xl) 0 var(--space-lg);
  padding: 0 0 var(--space-sm);
  border-bottom: 2px solid var(--border-subtle);
  font-family: var(--font-heading);
  font-size: clamp(22px, 2.5vw, 28px);
  font-weight: 800;
  line-height: 1.4;
  letter-spacing: -0.015em;
  color: var(--text-1);
}

.chapter h2::after {
  content: "";
  position: absolute;
  bottom: -2px;
  inset-inline-start: 0;
  width: 60px;
  height: 3px;
  background: linear-gradient(90deg, var(--primary), var(--accent));
  border-radius: var(--r-full);
}

.chapter h3 {
  margin: var(--space-2xl) 0 var(--space-md);
  font-family: var(--font-heading);
  font-size: 21px;
  font-weight: 700;
  line-height: 1.5;
  color: var(--text-1);
}

.chapter h3::before {
  content: "";
  display: inline-block;
  width: 5px;
  height: 18px;
  margin-inline-end: var(--space-sm);
  vertical-align: -3px;
  border-radius: var(--r-xs);
  background: linear-gradient(180deg, var(--primary), var(--accent));
}

.chapter h4 {
  margin: var(--space-xl) 0 var(--space-sm);
  font-family: var(--font-heading);
  font-size: 17px;
  font-weight: 650;
  color: var(--text-1);
}

.chapter h5 {
  margin: var(--space-lg) 0 var(--space-sm);
  font-family: var(--font-heading);
  font-size: 15px;
  font-weight: 600;
  color: var(--text-2);
}

.chapter p {
  margin: var(--space-md) 0;
  line-height: 1.9;
  color: var(--text-1);
  font-size: 16px;
}

.chapter ul,
.chapter ol {
  margin: var(--space-md) 0;
  padding-inline-start: var(--space-2xl);
}

.chapter li {
  margin: var(--space-sm) 0;
  padding-inline-start: var(--space-sm);
  line-height: 1.8;
}

.chapter li::marker { color: var(--primary); }

.chapter strong,
.chapter b { font-weight: 650; color: var(--text-1); }

.chapter em { font-style: normal; color: var(--text-2); }

.chapter code:not(pre code) {
  font-family: var(--font-mono);
  font-size: 0.875em;
  font-weight: 500;
  padding: 3px 8px;
  color: var(--brand-700);
  background: var(--primary-soft);
  border: 1px solid rgba(79,70,229,.1);
  border-radius: var(--r-sm);
  white-space: nowrap;
  direction: ltr;
  unicode-bidi: embed;
}

[data-theme="dark"] .chapter code:not(pre code) {
  color: #c7d2fe;
  background: rgba(99,102,241,.14);
  border-color: rgba(129,140,248,.2);
}

/* Callouts - Claymorphism style */
.callout {
  position: relative;
  margin: var(--space-xl) 0;
  padding: var(--space-lg) var(--space-xl);
  border: 1px solid var(--border-subtle);
  border-inline-start: 5px solid var(--primary);
  border-radius: var(--r-xl);
  box-shadow: var(--shadow-sm), var(--shadow-inner);
  overflow: hidden;
  transition: all var(--dur-3) var(--ease);
}

.callout:hover {
  box-shadow: var(--shadow-md), var(--shadow-inner);
  transform: translateY(-2px);
}

.callout .ctitle {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  margin-bottom: var(--space-md);
  font-family: var(--font-heading);
  font-size: 15px;
  font-weight: 700;
}

.callout.concept { background: var(--c-concept-bg); border-color: var(--c-concept-br); color: var(--c-concept-tx); }
.callout.pitfall { background: var(--c-pitfall-bg); border-color: var(--c-pitfall-br); color: var(--c-pitfall-tx); }
.callout.note { background: var(--c-note-bg); border-color: var(--c-note-br); color: var(--c-note-tx); }
.callout.advanced { background: var(--c-advanced-bg); border-color: var(--c-advanced-br); color: var(--c-advanced-tx); }
.callout.practice { background: var(--c-practice-bg); border-color: var(--c-practice-br); color: var(--c-practice-tx); }
.callout.analysis { background: var(--c-analysis-bg); border-color: var(--c-analysis-br); color: var(--c-analysis-tx); }

.callout.concept .ctitle { color: var(--c-concept-tx); }
.callout.pitfall .ctitle { color: var(--c-pitfall-tx); }
.callout.note .ctitle { color: var(--c-note-tx); }
.callout.advanced .ctitle { color: var(--c-advanced-tx); }
.callout.practice .ctitle { color: var(--c-practice-tx); }
.callout.analysis .ctitle { color: var(--c-analysis-tx); }

.callout p,
.callout li { color: var(--text-1); }

/* ============ 7. Data Tables (Responsive, Claymorphism) ============ */
.table-wrap {
  width: 100%;
  max-width: 100%;
  margin: var(--space-xl) 0;
  overflow-x: auto;
  overflow-y: hidden;
  overscroll-behavior-inline: contain;
  direction: ltr;
  border: 1px solid var(--border-default);
  border-radius: var(--r-xl);
  background: var(--bg-surface);
  box-shadow: var(--shadow-sm);
  scrollbar-width: thin;
  scrollbar-color: var(--border-strong) transparent;
}

.chapter table {
  width: 100%;
  direction: rtl;
  border-collapse: separate;
  border-spacing: 0;
  font-size: 14px;
  background: var(--bg-surface);
}

/* Structurally wide tables (4+ columns): preserve intrinsic width for horizontal scroll */
.chapter table:has(thead th:nth-child(4)) {
  min-width: max-content;
}

.chapter thead th {
  position: sticky;
  top: 0;
  padding: var(--space-md) var(--space-lg);
  text-align: start;
  font-size: 13px;
  font-weight: 650;
  letter-spacing: 0.02em;
  color: #fff;
  background: linear-gradient(120deg, var(--brand-700), var(--brand-600));
  border-bottom: 1px solid var(--border-default);
  white-space: nowrap;
}

.chapter tbody td {
  padding: var(--space-md) var(--space-lg);
  text-align: start;
  color: var(--text-1);
  border-bottom: 1px solid var(--border-subtle);
  vertical-align: top;
  line-height: 1.7;
}

.chapter tbody tr:last-child td { border-bottom: 0; }
.chapter tbody tr { transition: background var(--dur-1); }
.chapter tbody tr:hover td { background: var(--primary-soft); }

[data-theme="dark"] .chapter tbody tr:hover td { background: rgba(99,102,241,.08); }

/* ============ 8. Controls, Quiz, Answer Keys, Pager (Claymorphism) ============ */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-sm);
  min-height: 48px;
  padding: 0 var(--space-xl);
  border-radius: var(--r-lg);
  font-family: var(--font-heading);
  font-weight: 600;
  font-size: 15px;
  box-shadow: var(--shadow-sm);
  transition: all var(--dur-2) var(--ease);
  border: none;
  cursor: pointer;
}

.btn:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.btn:active { transform: translateY(0) scale(0.98); }

.btn.outline {
  background: var(--bg-surface);
  color: var(--primary);
  border: 2px solid var(--border-default);
  box-shadow: var(--shadow-sm);
}

.btn.outline:hover {
  background: var(--primary-soft);
  border-color: var(--primary);
  color: var(--primary);
}

.chapter .btn.outline {
  background: var(--accent);
  border-color: var(--accent-600);
  color: var(--color-on-accent);
}

.chapter .btn.outline:hover {
  background: var(--accent-400);
  border-color: var(--accent-500);
  color: var(--color-on-accent);
}

.chapter-body .quiz-btn.check {
  background: var(--accent-soft);
  border-color: var(--accent-500);
  color: var(--accent-soft-text);
  font-weight: 700;
}

.chapter-body .quiz-btn.check:hover {
  background: var(--accent);
  border-color: var(--accent-600);
  color: var(--color-on-accent);
}

.chapter-body .quiz-btn.primary {
  background: var(--accent);
  border-color: var(--accent-600);
  color: var(--color-on-accent);
}

.chapter-body .quiz-btn.primary:hover {
  background: var(--accent-400);
  border-color: var(--accent-500);
  color: var(--color-on-accent);
}

.chapter-body .quiz-toolbar .quiz-badge { color: var(--accent-contrast); }

.btn.success { background: var(--success); color: white; }
.btn.success.marked {
  background: var(--bg-inset);
  color: var(--text-2);
  border: 1px solid var(--border-default);
  box-shadow: none;
}

.chapter-actions {
  display: flex;
  gap: var(--space-md);
  flex-wrap: wrap;
  margin: var(--space-2xl) 0 var(--space-lg);
  padding-top: var(--space-lg);
  border-top: 1px solid var(--border-subtle);
}

.answer-key {
  margin: var(--space-lg) 0;
  padding: 0 var(--space-xl);
  max-height: 0;
  overflow: hidden;
  opacity: 0;
  background: var(--success-bg);
  border-inline-start: 4px solid var(--success);
  border-radius: var(--r-xl);
  transition: max-height var(--dur-3) var(--ease), padding var(--dur-3) var(--ease), opacity var(--dur-2);
}

.answer-key.show {
  max-height: 5000px;
  padding: var(--space-lg) var(--space-xl);
  opacity: 1;
  margin-top: var(--space-md);
}

.answer-key h4 {
  margin-top: 0;
  color: var(--success-text);
  font-family: var(--font-heading);
}

.quiz-item {
  margin: var(--space-sm) 0;
  padding: var(--space-md);
  border: 1px solid transparent;
  border-radius: var(--r-lg);
  transition: all var(--dur-2) var(--ease);
  background: var(--bg-inset);
}

.quiz-item:hover {
  border-color: var(--border-default);
  box-shadow: var(--shadow-sm);
}

.quiz-choice {
  border-radius: var(--r-full);
  transition: all var(--dur-2) var(--ease);
}

.quiz-choice:hover {
  transform: translateY(-1px);
  box-shadow: var(--shadow-sm);
}

.quiz-toolbar { padding-top: var(--space-md); margin-top: var(--space-lg); }
.quiz-explain { border-radius: var(--r-lg); background: var(--bg-inset); padding: var(--space-md); }

.quiz-stats {
  display: flex;
  gap: var(--space-md);
  flex-wrap: wrap;
}

.quiz-stats > div {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--space-xs);
  padding: var(--space-md) var(--space-lg);
  border-radius: var(--r-xl);
  background: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  box-shadow: var(--shadow-sm);
  min-width: 100px;
  transition: all var(--dur-2) var(--ease);
}

.quiz-stats > div:hover { box-shadow: var(--shadow-md); transform: translateY(-2px); }

.prod-box {
  border-radius: var(--r-xl);
  border-color: var(--border-default);
  box-shadow: var(--shadow-sm);
  background: var(--bg-surface);
  transition: all var(--dur-3) var(--ease);
}

.prod-box:hover { box-shadow: var(--shadow-md); }

.prod-text { border-radius: var(--r-lg); }

.pager {
  display: flex;
  gap: var(--space-md);
  margin: var(--space-2xl) 0 var(--space-lg);
  justify-content: center;
  flex-wrap: wrap;
}

.pager-btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-md) var(--space-xl);
  border-radius: var(--r-xl);
  font-family: var(--font-heading);
  font-weight: 600;
  box-shadow: var(--shadow-sm);
  transition: all var(--dur-2) var(--ease);
  background: var(--bg-surface);
  border: 1px solid var(--border-default);
  color: var(--text-1);
}

.pager-btn:hover {
  box-shadow: var(--shadow-md);
  background: var(--primary-soft);
  border-color: var(--primary);
  color: var(--primary);
  transform: translateY(-2px);
}

/* ============ 9. Footer (Fixed at bottom, Claymorphism) ============ */
.app-footer {
  padding: var(--space-lg) var(--space-xl);
  background: var(--bg-surface);
  border-top: 1px solid var(--border-subtle);
  color: var(--text-3);
  flex-shrink: 0;
}

.footer-content {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: var(--space-lg);
  flex-wrap: wrap;
  max-width: 1200px;
  margin: 0 auto;
}

.footer-copyright {
  font-size: 14px;
  color: var(--text-3);
  font-weight: 500;
}

.footer-contact {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-sm) var(--space-lg);
  border-radius: var(--r-full);
  background: var(--primary-soft);
  color: var(--primary);
  font-size: 14px;
  font-weight: 600;
  text-decoration: none;
  transition: all var(--dur-2) var(--ease);
  border: 1px solid var(--border-default);
}

.footer-contact:hover {
  background: var(--primary);
  color: var(--color-on-primary);
  text-decoration: none;
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
  border-color: var(--primary);
}

@media (max-width: 640px) {
  .footer-content { flex-direction: column; text-align: center; }
  .footer-contact { width: 100%; justify-content: center; }
}

/* ============ 10. Home, Dashboard, Index, and Learning Tools (Claymorphism) ============ */
.home-hero {
  padding: var(--space-3xl) var(--space-lg) var(--space-4xl);
  text-align: center;
}

.home-hero h1 {
  font-family: var(--font-heading);
  font-size: clamp(36px, 6vw, 56px);
  font-weight: 800;
  letter-spacing: -0.03em;
  line-height: 1.2;
  background-image: linear-gradient(135deg, var(--primary), var(--accent));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  margin-bottom: var(--space-lg);
}

.home-hero p {
  max-width: 65ch;
  margin: 0 auto;
  color: var(--text-2);
  font-size: clamp(16px, 1.8vw, 20px);
  line-height: 1.8;
}

.phase-grid {
  display: grid;
  gap: var(--space-lg);
  margin-top: var(--space-2xl);
  grid-template-columns: repeat(auto-fill, minmax(min(100%, 280px), 1fr));
}

.phase-card {
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  padding: var(--space-xl);
  border-radius: var(--r-2xl);
  background: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  box-shadow: var(--shadow-sm), var(--shadow-inner);
  transition: all var(--dur-3) var(--ease-spring);
  cursor: pointer;
}

.phase-card:hover {
  transform: translateY(-6px);
  box-shadow: var(--shadow-xl), var(--shadow-inner);
  border-color: var(--brand-200);
}

.pc-num {
  font-family: var(--font-heading);
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--primary);
  background: var(--primary-soft);
  padding: var(--space-xs) var(--space-md);
  border-radius: var(--r-full);
  margin-bottom: var(--space-md);
}

.phase-card h3 {
  font-family: var(--font-heading);
  font-size: 22px;
  font-weight: 700;
  color: var(--text-1);
  margin-bottom: var(--space-sm);
}

.pc-level {
  display: inline-block;
  font-size: 12px;
  font-weight: 600;
  padding: var(--space-xs) var(--space-md);
  border-radius: var(--r-full);
  background: var(--accent-soft);
  color: var(--accent-soft-text);
  margin-bottom: var(--space-md);
}

.phase-card p {
  color: var(--text-2);
  font-size: 15px;
  line-height: 1.7;
  margin: 0;
}

.quiz-stats > div,
.db-panel,
.db-phase,
.db-cp,
.idx-tools,
.prod-entry {
  border-radius: var(--r-xl);
  background: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  box-shadow: var(--shadow-sm);
  transition: all var(--dur-3) var(--ease);
}

.db-panel:hover,
.db-phase:hover {
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
}

.idx-tools {
  background: color-mix(in srgb, var(--bg-elevated) 92%, transparent);
  backdrop-filter: blur(8px);
  border-color: var(--border-default);
}

/* ============ 11. Source-added Lesson Fragments ============ */
.chapter-body div.src-add {
  display: flow-root;
  margin-block: var(--space-lg);
}

.chapter-body div.src-add > :first-child { margin-top: 0; }
.chapter-body div.src-add > :last-child { margin-bottom: 0; }
.chapter-body div.src-add div.src-add { margin-block: var(--space-sm); }

.chapter-body blockquote {
  margin: var(--space-xl) 0;
  padding: var(--space-lg) var(--space-xl);
  border-inline-start: 4px solid var(--brand-400);
  border-radius: var(--r-xl);
  background: var(--bg-inset);
  color: var(--text-1);
  font-family: var(--font-body);
  font-size: 0.97em;
  line-height: 1.9;
  direction: ltr;
  text-align: left;
  unicode-bidi: plaintext;
  box-shadow: var(--shadow-sm), var(--shadow-inner);
}

.chapter-body blockquote :last-child { margin-bottom: 0; }

/* ============ 12. Responsive Layout (Mobile-First, Claymorphism) ============ */

/* Tablet landscape / small desktop */
@media (max-width: 1180px) {
  #main {
    max-width: calc(100% - var(--space-lg));
    padding-inline: var(--space-lg);
  }
  .chapter-layout {
    grid-template-columns: minmax(0, 1fr);
    gap: var(--space-lg);
  }
  .chapter-toc {
    position: relative;
    top: auto;
    order: -1;
    max-height: min(42vh, 360px);
    border: 1px solid var(--border-default);
    border-radius: var(--r-lg);
    padding: var(--space-md);
    background: var(--bg-surface);
  }
}

/* Tablet portrait / mobile landscape - Sidebar becomes drawer */
@media (max-width: 960px) {
  .menu-toggle { display: flex; }
  .m-search-btn { display: flex; }
  .sidebar-collapse-btn { display: none !important; }

  #sidebar {
    position: fixed;
    inset-inline-end: 0;
    top: var(--header-h);
    width: var(--sidebar-w);
    max-width: 86vw;
    height: calc(100vh - var(--header-h));
    transform: translateX(-105%);
    z-index: 90;
    box-shadow: var(--shadow-xl);
    border-inline-start: 1px solid var(--sb-border);
  }

  [dir="ltr"] #sidebar { transform: translateX(-105%); }

  #sidebar.open { transform: translateX(0); }

  body.sidebar-open::before {
    content: "";
    position: fixed;
    inset: var(--header-h) 0 0;
    background: rgba(2,6,23,.52);
    backdrop-filter: blur(4px);
    z-index: 89;
  }

  .layout { grid-template-columns: minmax(0, 1fr); }
  .layout.sidebar-collapsed { grid-template-columns: minmax(0, 1fr); }

  #main {
    max-width: 100%;
    padding: var(--space-lg) var(--space-md) var(--space-3xl);
  }

  .chapter-header {
    padding: var(--space-xl) var(--space-lg);
    border-radius: var(--r-xl);
  }

  .site-title { display: none; }
}

/* Mobile portrait */
@media (max-width: 640px) {
  .app-header { padding-inline: var(--space-md); gap: var(--space-sm); }

  .search-wrap { display: none; }

  body.m-searching .search-wrap {
    display: block;
    position: fixed;
    top: var(--header-h);
    inset-inline: 0;
    max-width: none;
    z-index: 150;
    padding: var(--space-md) var(--space-lg);
    background: var(--bg-surface);
    border-bottom: 1px solid var(--border-default);
    box-shadow: var(--shadow-md);
  }

  body.m-searching .search-wrap::before { display: none; }

  body.m-searching .search-results { inset-inline: var(--space-lg); }

  #main { padding: var(--space-md) var(--space-sm) var(--space-2xl); }

  .chapter-header {
    padding: var(--space-lg) var(--space-md);
    border-radius: var(--r-lg);
  }

  .chapter-header h1 { font-size: clamp(24px, 6vw, 30px); }

  .chapter-body {
    padding: var(--space-lg) var(--space-md);
    border-radius: var(--r-lg);
  }

  .chapter h2 { font-size: clamp(20px, 4vw, 24px); margin-top: var(--space-2xl); }
  .chapter h3 { font-size: clamp(18px, 3.5vw, 20px); margin-top: var(--space-xl); }

  .callout { padding: var(--space-md) var(--space-lg); }

  .chapter thead th,
  .chapter tbody td { padding: var(--space-sm) var(--space-md); }

  .quiz-stats { grid-template-columns: repeat(2, minmax(0, 1fr)); }

  .db-hero { padding: var(--space-lg); gap: var(--space-lg); }
  .db-grid2 { grid-template-columns: 1fr; }

  .pager { grid-template-columns: 1fr 1fr; gap: var(--space-sm); }
  .pager-pos { display: none; }
  .pager-btn { padding: var(--space-sm) var(--space-md); }
  .pager-t { white-space: normal; font-size: 12px; }

  .chapter-toc { max-height: 40vh; }
}

/* Small mobile */
@media (max-width: 420px) {
  .logo-text { display: none; }
  .header-actions { gap: var(--space-xs); }
  .icon-btn { width: 40px; height: 40px; }
  .phase-grid { grid-template-columns: 1fr; }
  #main { padding-inline: var(--space-sm); }
  .chapter-body { padding: var(--space-md) var(--space-sm); }

  .home-hero h1 { font-size: clamp(28px, 7vw, 36px); }
  .home-hero p { font-size: 15px; }
}

/* ============ 13. Motion & Animation (Claymorphism: soft, spring) ============ */
.motion-pending,
.motion-row-pending {
  opacity: 0;
  transform: translate3d(0, 16px, 0);
  transition: opacity 0.5s var(--ease-out), transform 0.5s var(--ease-out);
  will-change: opacity, transform;
}

.motion-row-pending { transform: translate3d(16px, 0, 0); }

.motion-pending.motion-visible,
.motion-row-pending.motion-visible {
  opacity: 1 !important;
  transform: none !important;
  will-change: auto;
}

/* Staggered entrance for lists */
.stagger > * { opacity: 0; transform: translateY(12px); animation: staggerIn 0.5s var(--ease-out) forwards; }
.stagger > *:nth-child(1) { animation-delay: 0ms; }
.stagger > *:nth-child(2) { animation-delay: 80ms; }
.stagger > *:nth-child(3) { animation-delay: 160ms; }
.stagger > *:nth-child(4) { animation-delay: 240ms; }
.stagger > *:nth-child(5) { animation-delay: 320ms; }
.stagger > *:nth-child(6) { animation-delay: 400ms; }

@keyframes staggerIn {
  to { opacity: 1; transform: none; }
}

/* Respect reduced motion */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
  .motion-pending, .motion-row-pending { opacity: 1; transform: none; will-change: auto; }
  .stagger > * { opacity: 1; transform: none; animation: none; }
}

/* ============ 14. Print Styles ============ */
@media print {
  .chapter-toc,
  .reading-progress,
  .app-header,
  .app-footer,
  #sidebar,
  .menu-toggle,
  .m-search-btn,
  .search-wrap,
  .header-actions,
  .chapter-actions,
  .pager,
  .quiz-toolbar,
  .answer-key { display: none !important; }

  .chapter-layout { display: block; }
  .chapter-body { padding: 0; border: 0; box-shadow: none; background: transparent; }
  .layout { display: block; }
  #main { max-width: 100%; padding: 0; }
  .chapter-header { border: 0; box-shadow: none; background: none; color: var(--text-1); }
  .chapter-header h1 { color: var(--text-1); text-shadow: none; }
  .chapter-header p { color: var(--text-2); }
  .phase-label { background: var(--primary-soft); color: var(--primary); border: 1px solid var(--border-default); }
}

/* ============ 15. Dashboard Actions (Export/Import Buttons) ============ */
.db-actions {
  display: flex;
  gap: var(--space-sm);
  margin-top: var(--space-lg);
  flex-wrap: wrap;
}

.db-actions .btn {
  font-size: 13px;
  padding: 0 var(--space-lg);
  min-height: 40px;
  border-radius: var(--r-lg);
}

/* Additional responsive tweaks for very narrow screens */
@media (max-width: 480px) {
  .chapter-body,
  .answer-key,
  .callout,
  .table-wrap {
    padding: var(--space-sm) var(--space-md);
  }
}



/* ============ 16. Purchase & Contact Page ============ */
.purchase-options {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(100%, 300px), 1fr));
  gap: var(--space-lg);
  margin: var(--space-xl) 0;
}

.purchase-card {
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  padding: var(--space-xl);
  border-radius: var(--r-2xl);
  background: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  box-shadow: var(--shadow-sm), var(--shadow-inner);
  transition: all var(--dur-3) var(--ease);
}

.purchase-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg), var(--shadow-inner);
  border-color: var(--brand-200);
}

.purchase-card-icon {
  font-size: 3rem;
  margin-bottom: var(--space-md);
}

.purchase-card h3 {
  font-family: var(--font-heading);
  font-size: 22px;
  font-weight: 700;
  color: var(--text-1);
  margin-bottom: var(--space-sm);
}

.purchase-card p {
  color: var(--text-2);
  font-size: 15px;
  line-height: 1.7;
  margin-bottom: var(--space-lg);
}

.purchase-btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-md) var(--space-xl);
  border-radius: var(--r-lg);
  font-family: var(--font-heading);
  font-weight: 600;
  font-size: 15px;
  background: var(--primary);
  color: #fff;
  text-decoration: none;
  box-shadow: var(--shadow-sm);
  transition: all var(--dur-2) var(--ease);
  border: none;
  cursor: pointer;
}

.purchase-btn:hover {
  background: var(--primary-hover);
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
  color: #fff;
  text-decoration: none;
}

.contact-methods {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(100%, 280px), 1fr));
  gap: var(--space-lg);
  margin: var(--space-xl) 0;
}

.contact-card {
  display: flex;
  align-items: center;
  gap: var(--space-md);
  padding: var(--space-lg);
  border-radius: var(--r-xl);
  background: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  box-shadow: var(--shadow-sm);
  text-decoration: none;
  transition: all var(--dur-2) var(--ease);
}

.contact-card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
  text-decoration: none;
}

.contact-whatsapp:hover {
  border-color: #25D366;
}

.contact-facebook:hover {
  border-color: #1877F2;
}

.contact-icon {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 56px;
  height: 56px;
  border-radius: var(--r-lg);
  flex-shrink: 0;
}

.contact-whatsapp .contact-icon {
  background: rgba(37, 211, 102, .12);
  color: #25D366;
}

.contact-facebook .contact-icon {
  background: rgba(24, 119, 242, .12);
  color: #1877F2;
}

.contact-info h3 {
  font-family: var(--font-heading);
  font-size: 17px;
  font-weight: 700;
  color: var(--text-1);
  margin-bottom: 2px;
}

.contact-info p {
  font-size: 14px;
  color: var(--text-2);
  margin: 0;
}

/* Purchase Page Animations */
.purchase-page .motion-item {
  opacity: 0;
  transform: translateY(20px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

.purchase-page .motion-item.motion-visible {
  opacity: 1;
  transform: translateY(0);
}

.purchase-page .purchase-card {
  transition: transform 0.3s ease, box-shadow 0.3s ease, border-color 0.3s ease;
}

.purchase-page .purchase-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg), var(--shadow-inner);
  border-color: var(--brand-200);
}

.purchase-page .purchase-btn {
  transition: transform 0.2s ease, box-shadow 0.2s ease, background 0.2s ease;
}

.purchase-page .purchase-btn:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.purchase-page .purchase-btn:active {
  transform: translateY(0);
}

.purchase-page .contact-card {
  transition: transform 0.2s ease, box-shadow 0.2s ease, border-color 0.2s ease;
}

.purchase-page .contact-card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.purchase-page .contact-whatsapp:hover {
  border-color: #25D366;
}

.purchase-page .contact-facebook:hover {
  border-color: #1877F2;
}

/* Reduced motion */
@media (prefers-reduced-motion: reduce) {
  .purchase-page .motion-item {
    opacity: 1;
    transform: none;
    transition: none;
  }
  .purchase-page .purchase-card,
  .purchase-page .purchase-btn,
  .purchase-page .contact-card {
    transition: none;
  }
}

/* 2. Main layout container */
/* 3. Sidebar and main content */
#sidebar,
#main {
  min-height: 0;
}