/* ═══════════════════════════════════════════════════════════════
   System Design & ML Playbook — Design System
   ═══════════════════════════════════════════════════════════════ */

/* ── Design Tokens ── */
:root {
  /* Backgrounds */
  --bg: #f8fafc;
  --bg-panel: #ffffff;
  --bg-elevated: #f1f5f9;
  --bg-hover: #e8f0fe;

  /* Text */
  --text: #0f172a;
  --text-muted: #64748b;
  --text-light: #94a3b8;

  /* Borders */
  --border: #e2e8f0;
  --border-strong: #cbd5e1;

  /* Brand */
  --primary: #0d9488;
  --primary-dark: #0f766e;
  --primary-light: #ccfbf1;
  --primary-glow: rgba(13, 148, 136, 0.18);

  /* Hero gradient */
  --hero-a: #0f172a;
  --hero-b: #0d4f5c;
  --hero-c: #064e3b;

  /* Shadows */
  --shadow-xs: 0 1px 2px rgba(0,0,0,.06);
  --shadow-sm: 0 1px 3px rgba(0,0,0,.08), 0 1px 2px rgba(0,0,0,.05);
  --shadow-md: 0 4px 16px rgba(0,0,0,.08), 0 2px 6px rgba(0,0,0,.04);
  --shadow-lg: 0 12px 40px rgba(0,0,0,.12), 0 4px 16px rgba(0,0,0,.06);
  --shadow-xl: 0 24px 64px rgba(0,0,0,.15), 0 8px 24px rgba(0,0,0,.08);
  --shadow-glow: 0 0 0 3px var(--primary-glow);

  /* Shape */
  --r-sm: 8px;
  --r-md: 12px;
  --r-lg: 16px;
  --r-xl: 20px;
  --r-pill: 999px;

  /* Motion */
  --ease: cubic-bezier(0.4, 0, 0.2, 1);
  --t-fast: 150ms var(--ease);
  --t-base: 200ms var(--ease);
  --t-slow: 350ms var(--ease);
  --t-theme: 400ms var(--ease);

  /* Nav */
  --nav-h: 58px;
  --nav-bg: rgba(248, 250, 252, 0.88);
  --nav-border: rgba(226, 232, 240, 0.8);
}

/* Dark mode overrides */
[data-theme="dark"] {
  --bg: #0f172a;
  --bg-panel: #1e293b;
  --bg-elevated: #334155;
  --bg-hover: #1e3a5f;

  --text: #f1f5f9;
  --text-muted: #94a3b8;
  --text-light: #64748b;

  --border: #334155;
  --border-strong: #475569;

  --primary: #2dd4bf;
  --primary-dark: #14b8a6;
  --primary-light: rgba(45, 212, 191, 0.12);
  --primary-glow: rgba(45, 212, 191, 0.2);

  --hero-a: #020617;
  --hero-b: #0c1a2e;
  --hero-c: #071a1a;

  --shadow-xs: 0 1px 2px rgba(0,0,0,.25);
  --shadow-sm: 0 1px 3px rgba(0,0,0,.3), 0 1px 2px rgba(0,0,0,.2);
  --shadow-md: 0 4px 16px rgba(0,0,0,.3), 0 2px 6px rgba(0,0,0,.2);
  --shadow-lg: 0 12px 40px rgba(0,0,0,.4), 0 4px 16px rgba(0,0,0,.3);
  --shadow-xl: 0 24px 64px rgba(0,0,0,.5), 0 8px 24px rgba(0,0,0,.35);

  --nav-bg: rgba(15, 23, 42, 0.9);
  --nav-border: rgba(51, 65, 85, 0.8);
}

/* ── Category Colors ── */
/* New category names matching HTML sections */
.cat-foundation           { --cat: #f97316; --cat-bg: #fff7ed; }
.cat-datastorage          { --cat: #8b5cf6; --cat-bg: #f5f3ff; }
.cat-apinetworking        { --cat: #3b82f6; --cat-bg: #eff6ff; }
.cat-cloudplatform        { --cat: #0284c7; --cat-bg: #f0f9ff; }
.cat-distributedsystems   { --cat: #0d9488; --cat-bg: #f0fdfa; }
.cat-searchanalytics      { --cat: #f59e0b; --cat-bg: #fffbeb; }
.cat-scalereliability     { --cat: #22c55e; --cat-bg: #f0fdf4; }
.cat-security             { --cat: #ef4444; --cat-bg: #fef2f2; }
.cat-aimachinelearning    { --cat: #ec4899; --cat-bg: #fdf2f8; }
.cat-specializedsystems   { --cat: #06b6d4; --cat-bg: #ecfeff; }
.cat-reference            { --cat: #6366f1; --cat-bg: #eef2ff; }

[data-theme="dark"] .cat-foundation         { --cat-bg: rgba(249,115,22,.12); }
[data-theme="dark"] .cat-datastorage        { --cat-bg: rgba(139,92,246,.12); }
[data-theme="dark"] .cat-apinetworking      { --cat-bg: rgba(59,130,246,.12); }
[data-theme="dark"] .cat-cloudplatform      { --cat-bg: rgba(2,132,199,.12); }
[data-theme="dark"] .cat-distributedsystems { --cat-bg: rgba(13,148,136,.12); }
[data-theme="dark"] .cat-searchanalytics    { --cat-bg: rgba(245,158,11,.12); }
[data-theme="dark"] .cat-scalereliability   { --cat-bg: rgba(34,197,94,.12); }
[data-theme="dark"] .cat-security           { --cat-bg: rgba(239,68,68,.12); }
[data-theme="dark"] .cat-aimachinelearning   { --cat-bg: rgba(236,72,153,.12); }
[data-theme="dark"] .cat-specializedsystems { --cat-bg: rgba(6,182,212,.12); }
[data-theme="dark"] .cat-reference          { --cat-bg: rgba(99,102,241,.12); }

/* ── Reset ── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html {
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--nav-h) + 1rem);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-family: "Inter", "Segoe UI", system-ui, -apple-system, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
  transition: background var(--t-theme), color var(--t-theme);
  min-height: 100vh;
  scrollbar-width: thin;
  scrollbar-color: var(--border-strong) transparent;
}

/* ════════════════════════════════
   TOPNAV
   ════════════════════════════════ */
.topnav {
  position: sticky;
  top: 0;
  z-index: 100;
  height: var(--nav-h);
  background: var(--nav-bg);
  border-bottom: 1px solid var(--nav-border);
  backdrop-filter: blur(16px) saturate(1.5);
  -webkit-backdrop-filter: blur(16px) saturate(1.5);
  transition: background var(--t-theme), border-color var(--t-theme);
}

.topnav-inner {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 1.25rem;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
}

.brand {
  display: flex;
  align-items: center;
  gap: 0.55rem;
  text-decoration: none;
  color: var(--text);
  font-weight: 700;
  font-size: 0.95rem;
  white-space: nowrap;
  flex-shrink: 0;
  transition: color var(--t-base);
}
.brand:hover { color: var(--primary); }
.brand-icon { color: var(--primary); flex-shrink: 0; transition: color var(--t-base); }

.nav-actions {
  display: flex;
  align-items: center;
  gap: 0.3rem;
  flex-shrink: 0;
}

/* Icon buttons */
.btn-icon {
  position: relative;
  background: none;
  border: none;
  color: var(--text-muted);
  cursor: pointer;
  padding: 0.45rem;
  border-radius: var(--r-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  transition: background var(--t-base), color var(--t-base);
  line-height: 1;
  font-size: inherit;
  font-family: inherit;
}
.btn-icon:hover { background: var(--bg-elevated); color: var(--text); }
.btn-icon:focus-visible { outline: 2px solid var(--primary); outline-offset: 2px; }

/* Dark mode icon swap */
.theme-toggle .icon-moon { display: none; }
[data-theme="dark"] .theme-toggle .icon-sun { display: none; }
[data-theme="dark"] .theme-toggle .icon-moon { display: block; }

/* Nav badge */
.nav-badge {
  position: absolute;
  top: 1px;
  right: 1px;
  background: var(--primary);
  color: white;
  font-size: 0.6rem;
  font-weight: 700;
  min-width: 15px;
  height: 15px;
  border-radius: var(--r-pill);
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 0 3px;
}

/* GitHub CTA */
.btn-github {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  background: var(--text);
  color: var(--bg) !important;
  border: none;
  border-radius: var(--r-sm);
  padding: 0.45rem 0.9rem;
  font-size: 0.82rem;
  font-weight: 600;
  font-family: inherit;
  text-decoration: none;
  cursor: pointer;
  transition: opacity var(--t-base), transform var(--t-base);
  white-space: nowrap;
  flex-shrink: 0;
}
.btn-github:hover { opacity: 0.84; transform: translateY(-1px); }

/* ════════════════════════════════
   HERO
   ════════════════════════════════ */
.hero {
  position: relative;
  overflow: clip;
  background: linear-gradient(135deg, var(--hero-a) 0%, var(--hero-b) 50%, var(--hero-c) 100%);
  padding: 4.5rem 1.25rem 5.5rem;
  color: white;
}

.hero-canvas {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  opacity: 0.35;
  pointer-events: none;
}

.hero-inner {
  position: relative;
  z-index: 1;
  max-width: 1200px;
  margin: 0 auto;
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  background: rgba(255,255,255,.1);
  border: 1px solid rgba(255,255,255,.2);
  border-radius: var(--r-pill);
  padding: 0.3rem 0.9rem;
  font-size: 0.75rem;
  font-weight: 600;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  margin-bottom: 1.4rem;
  backdrop-filter: blur(8px);
}

.badge-pulse {
  display: block;
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: #4ade80;
  flex-shrink: 0;
  animation: pulse 2.5s ease-in-out infinite;
}

@keyframes pulse {
  0%, 100% { opacity: 1; box-shadow: 0 0 0 0 rgba(74,222,128,.5); }
  50% { opacity: .7; box-shadow: 0 0 0 5px rgba(74,222,128,0); }
}

.hero-title {
  font-size: clamp(2.1rem, 5.5vw, 3.5rem);
  font-weight: 900;
  line-height: 1.1;
  letter-spacing: -0.025em;
  margin-bottom: 1.2rem;
}

.hero-highlight {
  background: linear-gradient(90deg, #4ade80 0%, #22d3ee 60%, #818cf8 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero-lead {
  font-size: 1.08rem;
  line-height: 1.72;
  opacity: .88;
  max-width: 660px;
  margin-bottom: 2rem;
}

/* Search */
.hero-search { margin-bottom: 1.2rem; }

.search-wrapper {
  position: relative;
  display: inline-flex;
  align-items: center;
  width: min(580px, 100%);
}

.search-icon {
  position: absolute;
  left: 1rem;
  color: rgba(255,255,255,.55);
  pointer-events: none;
  flex-shrink: 0;
}

#searchInput {
  width: 100%;
  background: rgba(255,255,255,.1);
  border: 1.5px solid rgba(255,255,255,.28);
  border-radius: var(--r-md);
  color: white;
  padding: 0.82rem 3rem 0.82rem 2.85rem;
  font-size: 0.97rem;
  font-family: inherit;
  outline: none;
  transition: background var(--t-base), border-color var(--t-base), box-shadow var(--t-base);
  backdrop-filter: blur(8px);
}
#searchInput::placeholder { color: rgba(255,255,255,.5); }
#searchInput:focus {
  background: rgba(255,255,255,.16);
  border-color: rgba(255,255,255,.55);
  box-shadow: 0 0 0 3px rgba(255,255,255,.1);
}

.search-shortcut {
  position: absolute;
  right: 0.85rem;
  background: rgba(255,255,255,.15);
  border: 1px solid rgba(255,255,255,.3);
  border-radius: 5px;
  color: rgba(255,255,255,.75);
  font-size: 0.72rem;
  padding: 0.15rem 0.42rem;
  pointer-events: none;
  font-family: inherit;
  transition: opacity var(--t-base);
}
#searchInput:focus ~ .search-shortcut { opacity: 0; }

/* Filter pills */
.filters {
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
}

.filter-btn {
  background: rgba(255,255,255,.1);
  border: 1px solid rgba(255,255,255,.22);
  border-radius: var(--r-pill);
  color: rgba(255,255,255,.88);
  padding: 0.35rem 0.85rem;
  font-size: 0.79rem;
  font-weight: 500;
  font-family: inherit;
  cursor: pointer;
  transition: background var(--t-base), border-color var(--t-base), color var(--t-base);
  white-space: nowrap;
}
.filter-btn:hover {
  background: rgba(255,255,255,.18);
  border-color: rgba(255,255,255,.42);
}
.filter-btn.active {
  background: white;
  color: var(--primary-dark);
  border-color: white;
  font-weight: 700;
}

/* ════════════════════════════════
   CONTAINER
   ════════════════════════════════ */
.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 1.25rem 5rem;
  position: relative;
  z-index: 1;
}

/* ════════════════════════════════
   STATS
   ════════════════════════════════ */
.stats {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0.75rem;
  margin-top: -3rem;
  margin-bottom: 1.75rem;
}

.stat-card {
  background: var(--bg-panel);
  border: 1px solid var(--border);
  border-radius: var(--r-lg);
  box-shadow: var(--shadow-md);
  padding: 1.1rem 0.9rem;
  text-align: center;
  transition: background var(--t-theme), border-color var(--t-theme), box-shadow var(--t-base), transform var(--t-base);
}

.stat-card--clickable { cursor: pointer; }
.stat-card--clickable:hover {
  border-color: var(--primary);
  box-shadow: var(--shadow-md), var(--shadow-glow);
  transform: translateY(-2px);
}
.stat-card--clickable:focus-visible {
  outline: 2px solid var(--primary);
  outline-offset: 2px;
}

.stat-icon { font-size: 1.45rem; margin-bottom: 0.35rem; }

.stat-value {
  font-size: 1.75rem;
  font-weight: 800;
  color: var(--primary-dark);
  line-height: 1;
  margin-bottom: 0.3rem;
  transition: color var(--t-theme);
}
[data-theme="dark"] .stat-value { color: var(--primary); }

.stat-label {
  font-size: 0.7rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.07em;
  color: var(--text-muted);
}

/* ════════════════════════════════
   PROGRESS
   ════════════════════════════════ */
.progress-section {
  background: var(--bg-panel);
  border: 1px solid var(--border);
  border-radius: var(--r-lg);
  padding: 1rem 1.25rem;
  margin-bottom: 1.5rem;
  transition: background var(--t-theme), border-color var(--t-theme);
}

.progress-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 0.6rem;
}

.progress-label {
  font-size: 0.78rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--text-muted);
}

.progress-pct {
  font-size: 0.9rem;
  font-weight: 700;
  color: var(--primary-dark);
  transition: color var(--t-theme);
}
[data-theme="dark"] .progress-pct { color: var(--primary); }

.progress-track {
  height: 8px;
  background: var(--bg-elevated);
  border-radius: var(--r-pill);
  overflow: hidden;
  transition: background var(--t-theme);
}

.progress-fill {
  height: 100%;
  border-radius: var(--r-pill);
  background: linear-gradient(90deg, var(--primary), #22d3ee);
  width: 0%;
  transition: width 700ms cubic-bezier(0.4, 0, 0.2, 1);
}

/* ════════════════════════════════
   LEARNING PATHS
   ════════════════════════════════ */
.paths-section { margin-bottom: 2rem; }

.section-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 0.9rem;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.section-title {
  font-size: 1.15rem;
  font-weight: 800;
  color: var(--text);
  letter-spacing: -0.01em;
}

.btn-clear-path {
  background: none;
  border: 1px solid var(--border);
  border-radius: var(--r-pill);
  color: var(--text-muted);
  font-size: 0.78rem;
  font-family: inherit;
  font-weight: 500;
  padding: 0.25rem 0.75rem;
  cursor: pointer;
  transition: border-color var(--t-base), color var(--t-base);
}
.btn-clear-path:hover { border-color: var(--primary); color: var(--primary); }

.paths-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.75rem;
}

.path-card {
  background: var(--bg-panel);
  border: 1.5px solid var(--border);
  border-radius: var(--r-lg);
  padding: 1rem 1.1rem;
  cursor: pointer;
  text-align: left;
  font-family: inherit;
  color: var(--text);
  display: flex;
  align-items: center;
  gap: 0.85rem;
  transition: border-color var(--t-base), box-shadow var(--t-base), background var(--t-theme), transform var(--t-base);
}
.path-card:hover {
  border-color: var(--primary);
  box-shadow: var(--shadow-glow);
  transform: translateY(-2px);
}
.path-card.active,
.path-card[aria-pressed="true"] {
  border-color: var(--primary);
  background: var(--primary-light);
  box-shadow: var(--shadow-glow);
}
.path-card:focus-visible { outline: 2px solid var(--primary); outline-offset: 2px; }

.path-emoji { font-size: 1.65rem; flex-shrink: 0; }

.path-info { flex: 1; min-width: 0; }
.path-info h3 { font-size: 0.9rem; font-weight: 700; margin-bottom: 0.18rem; }
.path-info p { font-size: 0.75rem; color: var(--text-muted); line-height: 1.4; }

.path-count {
  flex-shrink: 0;
  background: var(--bg-elevated);
  border-radius: var(--r-pill);
  font-size: 0.68rem;
  font-weight: 700;
  color: var(--text-muted);
  padding: 0.2rem 0.55rem;
  margin-left: auto;
  white-space: nowrap;
}

/* ════════════════════════════════
   TOPICS SECTION
   ════════════════════════════════ */
.topics-section { }

.view-controls {
  display: flex;
  gap: 0.2rem;
  background: var(--bg-elevated);
  border-radius: var(--r-sm);
  padding: 0.2rem;
  transition: background var(--t-theme);
}

.view-btn {
  background: none;
  border: none;
  cursor: pointer;
  padding: 0.3rem 0.5rem;
  border-radius: 5px;
  color: var(--text-muted);
  display: flex;
  align-items: center;
  transition: background var(--t-base), color var(--t-base);
  font-family: inherit;
}
.view-btn.active { background: var(--bg-panel); color: var(--text); box-shadow: var(--shadow-xs); }
.view-btn:hover { color: var(--text); }
.view-btn:focus-visible { outline: 2px solid var(--primary); outline-offset: 2px; }

/* ── Topic Grid ── */
.topic-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 0.85rem;
  margin-top: 0.75rem;
}

.topic-grid.list-view {
  grid-template-columns: 1fr;
}

/* ── Topic Card ── */
.topic-card {
  background: var(--bg-panel);
  border: 1px solid var(--border);
  border-radius: var(--r-lg);
  box-shadow: var(--shadow-sm);
  padding: 1.15rem;
  display: flex;
  flex-direction: column;
  position: relative;
  overflow: hidden;
  cursor: pointer;
  transition:
    transform var(--t-base),
    box-shadow var(--t-base),
    border-color var(--t-base),
    background var(--t-theme);
  animation: cardIn 280ms var(--ease) both;
}

@keyframes cardIn {
  from { opacity: 0; transform: translateY(10px); }
  to   { opacity: 1; transform: translateY(0); }
}

/* Category accent stripe */
.topic-card::before {
  content: "";
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 3px;
  background: var(--cat, var(--primary));
  border-radius: var(--r-lg) var(--r-lg) 0 0;
}

.topic-card:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-lg);
  border-color: var(--border-strong);
}

/* Read state */
.topic-card.is-read { border-color: rgba(34,197,94,.35); }
.topic-card.is-read::after {
  content: "✓ Read";
  position: absolute;
  top: 0.6rem; right: 0.6rem;
  background: rgba(34,197,94,.12);
  color: #16a34a;
  font-size: 0.65rem;
  font-weight: 700;
  padding: 0.18rem 0.5rem;
  border-radius: var(--r-pill);
  pointer-events: none;
}
[data-theme="dark"] .topic-card.is-read::after { color: #4ade80; background: rgba(34,197,94,.15); }

/* Card internals */
.card-top {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 0.5rem;
  margin-bottom: 0.6rem;
}

.card-category {
  font-size: 0.68rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.07em;
  color: var(--cat, var(--primary));
  background: var(--cat-bg, var(--primary-light));
  padding: 0.2rem 0.58rem;
  border-radius: var(--r-pill);
  line-height: 1.5;
  white-space: nowrap;
}

.card-actions {
  display: flex;
  gap: 0.15rem;
  opacity: 0;
  transition: opacity var(--t-base);
  flex-shrink: 0;
}
.topic-card:hover .card-actions,
.topic-card:focus-within .card-actions,
.topic-card.is-bookmarked .card-actions,
.topic-card.is-read .card-actions { opacity: 1; }

@media (hover: none) {
  .card-actions { opacity: 1; }
}

.card-action-btn {
  background: none;
  border: none;
  cursor: pointer;
  padding: 0.22rem 0.28rem;
  border-radius: var(--r-sm);
  color: var(--text-light);
  font-size: 0.9rem;
  line-height: 1;
  transition: background var(--t-base), color var(--t-base);
  font-family: inherit;
}
.card-action-btn:hover { color: var(--text); background: var(--bg-elevated); }
.card-action-btn.is-active { color: var(--primary); }

.card-content {
  display: flex;
  flex-direction: column;
  flex: 1;
}

/* Title row: icon + title side by side */
.card-title-row {
  display: flex;
  align-items: flex-start;
  gap: 0.55rem;
  margin-bottom: 0.4rem;
}

.card-icon {
  font-size: 1.3rem;
  flex-shrink: 0;
  margin-top: 0.05rem;
  line-height: 1.3;
}

.card-title {
  font-size: 0.97rem;
  font-weight: 700;
  line-height: 1.32;
  margin-bottom: 0;
  color: var(--text);
  transition: color var(--t-base);
}

.card-summary {
  font-size: 0.83rem;
  color: var(--text-muted);
  line-height: 1.55;
  margin-top: 0.35rem;
  margin-bottom: 0.5rem;
}

/* ── Subtopics list ── */
.card-subtopics {
  list-style: none;
  padding: 0;
  margin: 0 0 0.1rem;
  display: flex;
  flex-direction: column;
  gap: 0;
  flex: 1;
}

.card-subtopic {
  font-size: 0.75rem;
  color: var(--text-muted);
  line-height: 1.5;
  padding: 0.14rem 0 0.14rem 1rem;
  position: relative;
  border-left: 2px solid var(--border);
  transition: color var(--t-base), border-color var(--t-base);
}
.card-subtopic::before {
  content: "•";
  position: absolute;
  left: 0.3rem;
  color: var(--cat, var(--primary));
  font-size: 0.65rem;
}
.topic-card:hover .card-subtopic {
  border-left-color: var(--cat, var(--primary));
}
/* Collapse the list when there are many subtopics */
.card-subtopics .card-subtopic:nth-child(n+6) {
  display: none;
}
.card-subtopics.expanded .card-subtopic:nth-child(n+6) {
  display: list-item;
}

.card-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-top: 0.95rem;
  padding-top: 0.75rem;
  border-top: 1px solid var(--border);
  gap: 0.5rem;
}

.card-link {
  color: var(--primary-dark);
  font-size: 0.83rem;
  font-weight: 700;
  text-decoration: none;
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
  background: none;
  border: none;
  padding: 0;
  cursor: pointer;
  font-family: inherit;
  transition: gap var(--t-base), color var(--t-base);
}
[data-theme="dark"] .card-link { color: var(--primary); }
.card-link:hover { gap: 0.5rem; }

.card-difficulty {
  font-size: 0.68rem;
  font-weight: 700;
  padding: 0.18rem 0.52rem;
  border-radius: var(--r-pill);
  white-space: nowrap;
}
.diff-beginner  { background: rgba(34,197,94,.12);  color: #16a34a; }
.diff-mid       { background: rgba(245,158,11,.12); color: #d97706; }
.diff-advanced  { background: rgba(239,68,68,.12);  color: #dc2626; }
[data-theme="dark"] .diff-beginner { color: #4ade80; }
[data-theme="dark"] .diff-mid      { color: #fbbf24; }
[data-theme="dark"] .diff-advanced { color: #f87171; }

/* ── List view overrides ── */
.list-view .topic-card {
  flex-direction: row;
  align-items: center;
  gap: 1rem;
  padding: 0.75rem 1.15rem;
}
.list-view .topic-card::before {
  top: 0; bottom: 0; right: auto;
  width: 3px; height: auto;
  border-radius: var(--r-lg) 0 0 var(--r-lg);
}
.list-view .topic-card::after { top: 0.35rem; }
.list-view .card-top { margin-bottom: 0; flex-shrink: 0; }
.list-view .card-content { flex: 1; min-width: 0; flex-direction: row; align-items: center; gap: 1rem; }
.list-view .card-title-row { margin-bottom: 0; }
.list-view .card-icon { display: none; }
.list-view .card-title { font-size: 0.91rem; }
.list-view .card-summary { display: none; }
.list-view .card-subtopics { display: none; }
.list-view .card-footer { margin-top: 0; padding-top: 0; border-top: none; margin-left: auto; flex-shrink: 0; }

/* Search highlight */
mark {
  background: rgba(250,204,21,.38);
  border-radius: 2px;
  padding: 0 1px;
  color: inherit;
}
[data-theme="dark"] mark { background: rgba(250,204,21,.2); }

/* Empty state */
.empty-state {
  text-align: center;
  color: var(--text-muted);
  padding: 3.5rem 1rem;
  font-size: 0.95rem;
  grid-column: 1 / -1;
}

.link-btn {
  background: none;
  border: none;
  color: var(--primary-dark);
  font-size: inherit;
  font-family: inherit;
  font-weight: 600;
  cursor: pointer;
  text-decoration: underline;
  padding: 0;
  margin-left: 0.25rem;
}
[data-theme="dark"] .link-btn { color: var(--primary); }

/* ════════════════════════════════
   SIDEBAR
   ════════════════════════════════ */
.sidebar {
  position: fixed;
  top: 0; right: 0; bottom: 0;
  width: 340px;
  background: var(--bg-panel);
  border-left: 1px solid var(--border);
  box-shadow: var(--shadow-xl);
  z-index: 200;
  display: flex;
  flex-direction: column;
  transform: translateX(100%);
  transition: transform var(--t-slow), background var(--t-theme), border-color var(--t-theme);
}
/* Override hidden so we can still animate */
.sidebar[hidden] { display: flex !important; }
.sidebar.open { transform: translateX(0); }

.sidebar-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 1.15rem 1.2rem;
  border-bottom: 1px solid var(--border);
  flex-shrink: 0;
}
.sidebar-header h3 { font-size: 0.97rem; font-weight: 700; }

.bookmark-list {
  flex: 1;
  overflow-y: auto;
  padding: 0.65rem;
}

.bookmark-item {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.75rem 0.8rem;
  border-radius: var(--r-sm);
  text-decoration: none;
  color: var(--text);
  background: none;
  border: none;
  width: 100%;
  text-align: left;
  cursor: pointer;
  font-family: inherit;
  transition: background var(--t-base);
}
.bookmark-item:hover { background: var(--bg-elevated); }

.bookmark-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--cat, var(--primary));
  flex-shrink: 0;
}

.bookmark-cat { font-size: 0.68rem; font-weight: 700; color: var(--text-muted); text-transform: uppercase; letter-spacing: 0.05em; }
.bookmark-title { font-size: 0.88rem; font-weight: 600; margin-top: 0.1rem; }

.sidebar-empty {
  color: var(--text-muted);
  font-size: 0.87rem;
  padding: 2rem 1.2rem;
  text-align: center;
  line-height: 1.7;
}

.sidebar-backdrop {
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,.42);
  backdrop-filter: blur(3px);
  z-index: 199;
  opacity: 0;
  transition: opacity var(--t-slow);
}
.sidebar-backdrop.visible { opacity: 1; }
.sidebar-backdrop[hidden] { display: block !important; pointer-events: none; }

/* ════════════════════════════════
   QUIZ OVERLAY
   ════════════════════════════════ */
.quiz-overlay {
  position: fixed;
  inset: 0;
  background: rgba(15,23,42,.88);
  backdrop-filter: blur(14px) saturate(1.2);
  z-index: 300;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 1.25rem;
}

.quiz-overlay[hidden] { display: none !important; }

.quiz-card {
  background: var(--bg-panel);
  border: 1px solid var(--border);
  border-radius: var(--r-xl);
  box-shadow: var(--shadow-xl);
  width: 100%;
  max-width: 640px;
  display: flex;
  flex-direction: column;
  overflow: hidden;
  animation: popIn 280ms var(--ease);
}

@keyframes popIn {
  from { opacity: 0; transform: scale(0.95) translateY(10px); }
  to   { opacity: 1; transform: scale(1) translateY(0); }
}

.quiz-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 1rem 1.25rem;
  border-bottom: 1px solid var(--border);
}

.quiz-meta { display: flex; align-items: center; gap: 0.75rem; }

.quiz-label {
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.07em;
  color: var(--primary);
}

.quiz-pos {
  font-size: 0.82rem;
  font-weight: 500;
  color: var(--text-muted);
}

.quiz-body {
  padding: 2rem 2rem 1.5rem;
  flex: 1;
}

.quiz-cat-badge {
  display: inline-block;
  font-size: 0.7rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.07em;
  color: var(--cat, var(--primary));
  background: var(--cat-bg, var(--primary-light));
  padding: 0.2rem 0.6rem;
  border-radius: var(--r-pill);
  margin-bottom: 0.95rem;
}

.quiz-question {
  font-size: clamp(1.3rem, 3vw, 1.6rem);
  font-weight: 800;
  line-height: 1.25;
  margin-bottom: 1.5rem;
  color: var(--text);
  letter-spacing: -0.015em;
}

.quiz-hint {
  font-size: 0.83rem;
  color: var(--text-muted);
}
.quiz-hint kbd {
  background: var(--bg-elevated);
  border: 1px solid var(--border-strong);
  border-radius: 4px;
  padding: 0.1rem 0.35rem;
  font-size: 0.75rem;
  font-family: inherit;
}

.quiz-answer-block { margin-top: 0.5rem; }

.quiz-divider {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin-bottom: 0.9rem;
}
.quiz-divider::before,
.quiz-divider::after { content: ""; flex: 1; height: 1px; background: var(--border); }
.quiz-divider span {
  font-size: 0.68rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--text-muted);
}

.quiz-answer {
  font-size: 1rem;
  line-height: 1.68;
  color: var(--text-muted);
  margin-bottom: 1rem;
}

.quiz-link {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--primary-dark);
  text-decoration: none;
  transition: color var(--t-base);
}
[data-theme="dark"] .quiz-link { color: var(--primary); }
.quiz-link:hover { text-decoration: underline; }

/* Quiz footer */
.quiz-footer {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding: 1rem 1.25rem;
  border-top: 1px solid var(--border);
  flex-wrap: wrap;
}

.quiz-dots {
  flex: 1;
  display: flex;
  flex-wrap: wrap;
  gap: 4px;
  justify-content: center;
  padding: 0 0.5rem;
}

.quiz-dot {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--border-strong);
  transition: background var(--t-base);
}
.quiz-dot.active { background: var(--primary); transform: scale(1.3); }
.quiz-dot.done   { background: rgba(34,197,94,.5); }

/* Quiz buttons */
.btn-quiz {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--r-sm);
  color: var(--text);
  font-size: 0.84rem;
  font-weight: 600;
  font-family: inherit;
  padding: 0.5rem 1rem;
  cursor: pointer;
  transition: border-color var(--t-base), color var(--t-base), background var(--t-base);
  white-space: nowrap;
  flex-shrink: 0;
}
.btn-quiz--ghost:hover { border-color: var(--primary); color: var(--primary); }
.btn-quiz--primary {
  background: var(--primary);
  border-color: var(--primary);
  color: white;
}
.btn-quiz--primary:hover { background: var(--primary-dark); border-color: var(--primary-dark); }
.btn-quiz--done { background: #16a34a; border-color: #16a34a; color: white; }
.btn-quiz--done:hover { background: #15803d; border-color: #15803d; }

/* ════════════════════════════════
   SHORTCUTS MODAL
   ════════════════════════════════ */
.modal-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,.5);
  backdrop-filter: blur(4px);
  z-index: 400;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 1.25rem;
}

.modal-overlay[hidden] { display: none !important; }

.modal {
  background: var(--bg-panel);
  border: 1px solid var(--border);
  border-radius: var(--r-xl);
  box-shadow: var(--shadow-xl);
  width: 100%;
  max-width: 440px;
  overflow: hidden;
  animation: popIn 220ms var(--ease);
}

.modal-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 1.1rem 1.25rem;
  border-bottom: 1px solid var(--border);
}
.modal-header h3 { font-size: 0.97rem; font-weight: 700; }

.shortcuts-grid {
  padding: 1rem 1.25rem 1.25rem;
  display: flex;
  flex-direction: column;
  gap: 0.45rem;
}

.shortcut-row {
  display: flex;
  align-items: center;
  gap: 0.85rem;
}
.shortcut-row span { font-size: 0.88rem; color: var(--text-muted); }

kbd {
  background: var(--bg-elevated);
  border: 1px solid var(--border-strong);
  border-radius: 5px;
  box-shadow: 0 1px 0 var(--border-strong);
  color: var(--text);
  font-family: "Inter", monospace;
  font-size: 0.75rem;
  font-weight: 600;
  min-width: 26px;
  padding: 0.18rem 0.44rem;
  text-align: center;
  white-space: nowrap;
  flex-shrink: 0;
  display: inline-flex;
  align-items: center;
  justify-content: center;
}

/* ════════════════════════════════
   TOAST
   ════════════════════════════════ */
.toast {
  position: fixed;
  bottom: 1.5rem;
  left: 50%;
  transform: translateX(-50%) translateY(80px);
  background: var(--text);
  color: var(--bg);
  border-radius: var(--r-md);
  padding: 0.65rem 1.3rem;
  font-size: 0.87rem;
  font-weight: 500;
  box-shadow: var(--shadow-lg);
  z-index: 500;
  transition: transform var(--t-slow), opacity var(--t-slow);
  white-space: nowrap;
  pointer-events: none;
  opacity: 0;
}
.toast.show {
  transform: translateX(-50%) translateY(0);
  opacity: 1;
}

/* ════════════════════════════════
   FOOTER
   ════════════════════════════════ */
.footer {
  border-top: 1px solid var(--border);
  background: var(--bg-panel);
  padding: 2rem 1.25rem;
  transition: background var(--t-theme), border-color var(--t-theme);
}

.footer-inner {
  max-width: 1200px;
  margin: 0 auto;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.75rem;
  text-align: center;
}

.footer-brand {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-weight: 700;
  font-size: 0.95rem;
  color: var(--text);
}
.footer-brand svg { color: var(--primary); }

.footer-links {
  display: flex;
  gap: 1.5rem;
  flex-wrap: wrap;
  justify-content: center;
}
.footer-links a {
  color: var(--text-muted);
  text-decoration: none;
  font-size: 0.87rem;
  transition: color var(--t-base);
}
.footer-links a:hover { color: var(--primary); }

.footer-sub {
  color: var(--text-muted);
  font-size: 0.82rem;
}

/* ════════════════════════════════
   RESPONSIVE
   ════════════════════════════════ */
@media (max-width: 960px) {
  .stats { grid-template-columns: repeat(2, 1fr); }
  .paths-grid { grid-template-columns: 1fr; }
}

@media (max-width: 640px) {
  .hero { padding: 3rem 1rem 3.5rem; }
  .hero-title { font-size: 2rem; }
  .hero-lead { font-size: 0.97rem; }
  .stats { grid-template-columns: repeat(2, 1fr); margin-top: 0.5rem; }
  .brand-text { display: none; }
  .btn-github span { display: none; }
  .btn-github { padding: 0.45rem 0.55rem; }
  .sidebar { width: 100%; }
  .quiz-body { padding: 1.5rem 1.25rem 1rem; }
  .quiz-dots { display: none; }
  .topnav-inner { gap: 0.5rem; }
}

/* ════════════════════════════════
   SCROLLBAR
   ════════════════════════════════ */
::-webkit-scrollbar { width: 6px; height: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border-strong); border-radius: var(--r-pill); }
::-webkit-scrollbar-thumb:hover { background: var(--text-light); }

/* ════════════════════════════════
   FOCUS / ACCESSIBILITY
   ════════════════════════════════ */
:focus-visible { outline: 2px solid var(--primary); outline-offset: 2px; }
*:focus:not(:focus-visible) { outline: none; }

/* ════════════════════════════════
   PRINT
   ════════════════════════════════ */
@media print {
  .topnav, .hero-canvas, .card-actions, .quiz-overlay,
  .sidebar, .sidebar-backdrop, .toast, .modal-overlay,
  .hero-badge, .filters { display: none !important; }
  .stats { margin-top: 1rem; }
  .topic-card { break-inside: avoid; box-shadow: none; }
}

/* ════════════════════════════════
   REDUCE MOTION
   ════════════════════════════════ */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
  }
}

/* ════════════════════════════════
   READER PANEL
   ════════════════════════════════ */
.reader-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.55);
  backdrop-filter: blur(4px);
  z-index: 900;
  display: flex;
  align-items: stretch;
  justify-content: flex-end;
  animation: readerFadeIn 0.2s var(--ease);
}

.reader-overlay[hidden] { display: none !important; }

.reader-overlay.is-closing {
  animation: fadeOut 0.25s var(--ease) forwards;
}

.reader-overlay.is-closing .reader-panel {
  animation: slideOutRight 0.25s var(--ease) forwards;
}

@keyframes readerFadeIn {
  from { opacity: 0; }
  to   { opacity: 1; }
}

@keyframes fadeOut {
  from { opacity: 1; }
  to   { opacity: 0; }
}

@keyframes slideOutRight {
  from { transform: translateX(0); }
  to   { transform: translateX(100%); }
}

.reader-panel {
  width: min(780px, 100vw);
  height: 100dvh;
  background: var(--bg-panel);
  display: flex;
  flex-direction: column;
  box-shadow: var(--shadow-xl);
  animation: slideInRight 0.3s var(--ease);
  overflow: hidden;
}

@keyframes slideInRight {
  from { transform: translateX(100%); opacity: 0; }
  to   { transform: translateX(0);   opacity: 1; }
}

.reader-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 1rem 1.25rem;
  border-bottom: 1px solid var(--border);
  background: var(--bg-panel);
  flex-shrink: 0;
}

.reader-header-left {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  min-width: 0;
}

.reader-topic-icon {
  font-size: 1.6rem;
  flex-shrink: 0;
}

.reader-category {
  display: block;
  font-size: 0.72rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--primary);
  margin-bottom: 0.15rem;
}

.reader-title {
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--text);
  margin: 0;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  max-width: 520px;
}

.reader-header-actions {
  display: flex;
  align-items: center;
  gap: 0.25rem;
  flex-shrink: 0;
}

.reader-action-btn {
  font-size: 1rem;
  display: flex;
  align-items: center;
  justify-content: center;
}

.reader-action-btn.is-active {
  color: var(--primary);
  background: var(--primary-light);
}

.reader-body {
  flex: 1;
  overflow-y: auto;
  padding: 0;
  scroll-behavior: smooth;
  position: relative;
  scrollbar-width: thin;
  scrollbar-color: var(--border-strong) transparent;
}

.reader-content {
  padding: 2rem 2.25rem 3rem;
  max-width: 100%;
}

/* ── Reader Loading Spinner ── */
.reader-loading {
  position: absolute;
  inset: 0;
  z-index: 5;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 1rem;
  background: var(--bg-panel);
  color: var(--text-muted);
  font-size: 0.9rem;
}

.reader-loading[hidden] { display: none !important; }

.reader-spinner {
  width: 36px;
  height: 36px;
  border: 3px solid var(--border);
  border-top-color: var(--primary);
  border-radius: 50%;
  animation: spin 0.7s linear infinite;
  flex-shrink: 0;
}

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

/* ── Markdown Typography ── */
.reader-content h1 {
  font-size: 1.75rem;
  font-weight: 800;
  color: var(--text);
  margin: 0 0 0.5rem;
  line-height: 1.2;
}

.reader-content h2 {
  font-size: 1.3rem;
  font-weight: 700;
  color: var(--text);
  margin: 2.5rem 0 0.75rem;
  padding-bottom: 0.4rem;
  border-bottom: 2px solid var(--primary-light);
}

.reader-content h3 {
  font-size: 1.08rem;
  font-weight: 700;
  color: var(--text);
  margin: 1.75rem 0 0.5rem;
}

.reader-content h4 {
  font-size: 0.97rem;
  font-weight: 600;
  color: var(--text-muted);
  margin: 1.25rem 0 0.4rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

.reader-content p {
  color: var(--text);
  line-height: 1.75;
  margin: 0 0 1rem;
  font-size: 0.97rem;
}

.reader-content ul,
.reader-content ol {
  padding-left: 1.5rem;
  margin: 0 0 1rem;
  color: var(--text);
}

.reader-content li {
  line-height: 1.7;
  margin-bottom: 0.3rem;
  font-size: 0.97rem;
}

.reader-content li + li {
  margin-top: 0.2rem;
}

.reader-content strong {
  font-weight: 700;
  color: var(--text);
}

.reader-content em {
  font-style: italic;
}

.reader-content code {
  font-family: 'JetBrains Mono', 'Fira Code', 'Cascadia Code', 'Consolas', monospace;
  font-size: 0.84em;
  background: var(--bg-elevated);
  color: var(--primary-dark);
  padding: 0.15em 0.4em;
  border-radius: 4px;
  border: 1px solid var(--border);
}

.reader-content pre {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--r-md);
  padding: 1.25rem 1.5rem;
  overflow-x: auto;
  margin: 1.25rem 0;
  font-size: 0.875rem;
  line-height: 1.6;
}

.reader-content pre code {
  background: none;
  border: none;
  padding: 0;
  color: var(--text);
  font-size: inherit;
}

/* Tables */
.reader-content table {
  width: 100%;
  border-collapse: collapse;
  margin: 1.5rem 0;
  font-size: 0.9rem;
  border: 1px solid var(--border);
  border-radius: var(--r-md);
  overflow: hidden;
}

.reader-content th {
  background: var(--bg-elevated);
  font-weight: 700;
  font-size: 0.82rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--text-muted);
  padding: 0.65rem 1rem;
  text-align: left;
  border-bottom: 2px solid var(--border);
}

.reader-content td {
  padding: 0.65rem 1rem;
  border-bottom: 1px solid var(--border);
  color: var(--text);
  vertical-align: top;
  line-height: 1.5;
}

.reader-content tr:last-child td {
  border-bottom: none;
}

.reader-content tr:nth-child(even) td {
  background: var(--bg-elevated);
}

/* Blockquotes (tip/warning boxes) */
.reader-content blockquote {
  margin: 1.25rem 0;
  padding: 0.85rem 1.25rem;
  border-left: 4px solid var(--primary);
  background: var(--primary-light);
  border-radius: 0 var(--r-sm) var(--r-sm) 0;
  color: var(--text);
  font-size: 0.95rem;
  line-height: 1.65;
}

.reader-content blockquote p {
  margin: 0;
  color: inherit;
}

.reader-content blockquote p + p {
  margin-top: 0.4rem;
}

/* Warning blockquotes (those starting with ⚠️) */
.reader-content blockquote:has(p:first-child > strong:first-child) {
  border-left-color: #f59e0b;
  background: #fef3c7;
}

[data-theme="dark"] .reader-content blockquote:has(p:first-child > strong:first-child) {
  border-left-color: #f59e0b;
  background: rgba(245, 158, 11, 0.15);
}

/* Horizontal rules */
.reader-content hr {
  border: none;
  border-top: 1px solid var(--border);
  margin: 2rem 0;
}


.reader-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.75rem;
  padding: 0.875rem 1.25rem;
  border-top: 1px solid var(--border);
  background: var(--bg-panel);
  flex-shrink: 0;
}

/* ── Dark mode overrides for reader ── */
[data-theme="dark"] .reader-overlay {
  background: rgba(0, 0, 0, 0.72);
}

[data-theme="dark"] .reader-content code {
  background: rgba(255, 255, 255, 0.08);
  border-color: var(--border);
  color: #86efac;
}

[data-theme="dark"] .reader-content pre {
  background: #0d1117;
  border-color: var(--border);
}

.reader-content pre code.hljs {
  background: transparent;
  padding: 0;
  border: none;
}

[data-theme="dark"] .reader-content pre code {
  color: #e2e8f0;
}

[data-theme="dark"] .reader-content th {
  background: rgba(255, 255, 255, 0.05);
}

[data-theme="dark"] .reader-content tr:nth-child(even) td {
  background: rgba(255, 255, 255, 0.03);
}

[data-theme="dark"] .reader-content blockquote {
  background: rgba(13, 148, 136, 0.12);
}

/* ── Responsive reader ── */
@media (max-width: 640px) {
  .reader-panel {
    width: 100vw;
    border-radius: 0;
  }
  .reader-content {
    padding: 1.25rem 1rem 2rem;
  }
  .reader-title {
    max-width: 180px;
    font-size: 0.95rem;
  }
  .reader-content table {
    font-size: 0.8rem;
  }
  .reader-content th,
  .reader-content td {
    padding: 0.5rem 0.65rem;
  }
  .reader-footer {
    gap: 0.4rem;
  }
}

/* ════════════════════════════════
   COMPLETED SIDEBAR
   ════════════════════════════════ */
.completed-sidebar {
  position: fixed;
  top: 0; right: 0; bottom: 0;
  width: 380px;
  background: var(--bg-panel);
  border-left: 1px solid var(--border);
  box-shadow: var(--shadow-xl);
  z-index: 200;
  display: flex;
  flex-direction: column;
  transform: translateX(100%);
  transition: transform var(--t-slow), background var(--t-theme), border-color var(--t-theme);
}
.completed-sidebar[hidden] { display: flex !important; }
.completed-sidebar.open { transform: translateX(0); }

.completed-sidebar .sidebar-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 1.15rem 1.2rem;
  border-bottom: 1px solid var(--border);
  flex-shrink: 0;
}
.completed-sidebar .sidebar-header h3 { font-size: 0.97rem; font-weight: 700; }

.completed-list {
  flex: 1;
  overflow-y: auto;
  padding: 0.65rem;
  scrollbar-width: thin;
  scrollbar-color: var(--border-strong) transparent;
}

.completed-item {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.65rem 0.8rem;
  border-radius: var(--r-sm);
  text-decoration: none;
  color: var(--text);
  background: none;
  border: none;
  width: 100%;
  text-align: left;
  cursor: pointer;
  font-family: inherit;
  transition: background var(--t-base);
}
.completed-item:hover { background: var(--bg-elevated); }

.completed-check {
  width: 20px;
  height: 20px;
  border-radius: 50%;
  background: rgba(34,197,94,.12);
  color: #16a34a;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.7rem;
  flex-shrink: 0;
}
[data-theme="dark"] .completed-check { color: #4ade80; background: rgba(34,197,94,.18); }

.completed-item-info { flex: 1; min-width: 0; }
.completed-item-cat {
  font-size: 0.68rem;
  font-weight: 700;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}
.completed-item-title {
  font-size: 0.88rem;
  font-weight: 600;
  margin-top: 0.1rem;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.completed-item-remove {
  background: none;
  border: none;
  color: var(--text-light);
  cursor: pointer;
  padding: 0.2rem;
  border-radius: var(--r-sm);
  font-size: 0.75rem;
  opacity: 0;
  transition: opacity var(--t-base), color var(--t-base);
  flex-shrink: 0;
}
.completed-item:hover .completed-item-remove { opacity: 1; }
.completed-item-remove:hover { color: #ef4444; }

.completed-empty {
  color: var(--text-muted);
  font-size: 0.87rem;
  padding: 2.5rem 1.2rem;
  text-align: center;
  line-height: 1.7;
}

.completed-footer {
  padding: 0.85rem 1.2rem;
  border-top: 1px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-shrink: 0;
}
.completed-footer-text {
  font-size: 0.78rem;
  font-weight: 600;
  color: var(--text-muted);
}
.completed-footer-pct {
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--primary-dark);
}
[data-theme="dark"] .completed-footer-pct { color: var(--primary); }

@media (max-width: 640px) {
  .completed-sidebar { width: 100%; }
}

/* ════════════════════════════════
   BACK TO TOP
   ════════════════════════════════ */
.back-to-top {
  position: fixed;
  bottom: 1.5rem;
  right: 1.5rem;
  z-index: 50;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  background: var(--primary);
  color: white;
  border: none;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: var(--shadow-md);
  opacity: 0;
  transform: translateY(12px);
  pointer-events: none;
  transition: opacity var(--t-base), transform var(--t-base), background var(--t-base);
}
.back-to-top.visible {
  opacity: 1;
  transform: translateY(0);
  pointer-events: auto;
}
.back-to-top:hover {
  background: var(--primary-dark);
  transform: translateY(-2px);
}