/* ===== CSS VARIABLES / THEMING ===== */
:root {
  --font-body: 'Inter', system-ui, -apple-system, sans-serif;
  --font-code: 'Fira Code', 'Cascadia Code', 'Consolas', monospace;
  --sidebar-w: 280px;
  --header-h: 58px;
  --radius: 8px;
  --transition: .25s ease;
  --space-xs: 4px;
  --space-sm: 8px;
  --space-md: 16px;
  --space-lg: 24px;
  --space-xl: 32px;
  --space-2xl: 48px;
}

[data-theme="dark"] {
  --bg: #0f1117;
  --bg-card: #1a1d27;
  --bg-code: #141620;
  --bg-sidebar: #141620;
  --text: #e2e4e9;
  --text-muted: #9ca3af;
  --accent: #6c8cff;
  --accent2: #a78bfa;
  --border: #2a2d3a;
  --shadow: 0 2px 12px rgba(0,0,0,.4);
  --gotcha-bg: #2d1f1f;
  --gotcha-border: #e74c3c;
  --tip-bg: #1a2d1f;
  --tip-border: #2ecc71;
  --info-bg: rgba(108,140,255,.08);
  --scrollbar-thumb: #3a3d4a;
  --hover-bg: rgba(108,140,255,.06);
  --tag-bg: rgba(108,140,255,.12);
}

[data-theme="light"] {
  --bg: #f5f6fa;
  --bg-card: #ffffff;
  --bg-code: #f0f1f5;
  --bg-sidebar: #ffffff;
  --text: #1a1d27;
  --text-muted: #6b7280;
  --accent: #4a6cf7;
  --accent2: #7c5cbf;
  --border: #e0e2e9;
  --shadow: 0 2px 12px rgba(0,0,0,.08);
  --gotcha-bg: #fef2f2;
  --gotcha-border: #e74c3c;
  --tip-bg: #f0fdf4;
  --tip-border: #2ecc71;
  --info-bg: rgba(74,108,247,.06);
  --scrollbar-thumb: #c0c3cc;
  --hover-bg: rgba(74,108,247,.06);
  --tag-bg: rgba(74,108,247,.1);
}

/* ===== RESET ===== */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; scroll-padding-top: calc(var(--header-h) + 20px); }
body {
  font-family: var(--font-body);
  background: var(--bg);
  color: var(--text);
  line-height: 1.75;
  transition: background var(--transition), color var(--transition);
}

/* ===== PROGRESS BAR ===== */
#progress {
  position: fixed; top: 0; left: 0; height: 3px;
  background: linear-gradient(90deg, var(--accent), var(--accent2));
  z-index: 1001; transition: width .1s linear; width: 0;
}

/* ===== HEADER ===== */
.header {
  position: fixed; top: 0; left: 0; right: 0; height: var(--header-h);
  background: var(--bg-sidebar); border-bottom: 1px solid var(--border);
  display: flex; align-items: center; padding: 0 24px; z-index: 1000; gap: 16px;
}
.header h1 { font-size: 1.1rem; font-weight: 700; white-space: nowrap; }
.header h1 span { color: var(--accent); }
.header-nav { display: flex; gap: 8px; margin-left: auto; }
.header-nav a {
  color: var(--text-muted); text-decoration: none; font-size: .82rem;
  padding: 6px 12px; border-radius: var(--radius); transition: all var(--transition);
  border: 1px solid transparent;
}
.header-nav a:hover { color: var(--accent); border-color: var(--border); }
.theme-toggle {
  background: none; border: 1px solid var(--border); border-radius: var(--radius);
  padding: 6px 12px; cursor: pointer; color: var(--text); font-size: 1.1rem;
  transition: all var(--transition); display: flex; align-items: center; gap: 4px;
}
.theme-toggle:hover { border-color: var(--accent); color: var(--accent); }

/* ===== SIDEBAR (Topic Page) ===== */
.sidebar {
  position: fixed; top: var(--header-h); left: 0; width: var(--sidebar-w);
  height: calc(100vh - var(--header-h)); background: var(--bg-sidebar);
  border-right: 1px solid var(--border); overflow-y: auto; padding: 16px 0;
  z-index: 999; transition: transform var(--transition);
}
.sidebar a {
  display: block; padding: 8px 22px; color: var(--text-muted); text-decoration: none;
  font-size: .83rem; border-left: 3px solid transparent; transition: all var(--transition);
}
.sidebar a:hover, .sidebar a.active {
  color: var(--accent); border-left-color: var(--accent); background: var(--hover-bg);
}
.sidebar .nav-group { margin-bottom: 6px; }
.sidebar .nav-group-title {
  padding: 12px 22px 4px; font-size: .7rem; text-transform: uppercase;
  letter-spacing: .08em; color: var(--text-muted); font-weight: 600;
}
.sidebar .nav-back {
  display: flex; align-items: center; gap: 6px; padding: 10px 22px 14px;
  color: var(--accent); text-decoration: none; font-size: .85rem; font-weight: 500;
  border-bottom: 1px solid var(--border); margin-bottom: 8px;
}
.sidebar .nav-back:hover { background: var(--hover-bg); }

/* ===== MAIN CONTENT ===== */
.main {
  margin-left: var(--sidebar-w); margin-top: var(--header-h);
  padding: 36px 48px 100px; max-width: 980px;
}
.main.no-sidebar { margin-left: 0; max-width: 1200px; margin-inline: auto; }

/* ===== SECTION STYLES ===== */
.section { margin-bottom: 56px; }
.section h2 {
  font-size: 1.75rem; font-weight: 700; margin-bottom: 12px;
  padding-bottom: 10px; border-bottom: 3px solid var(--accent); display: inline-block;
}
.section h3 {
  font-size: 1.2rem; font-weight: 600; margin: 28px 0 10px; color: var(--accent2);
}
.section h4 {
  font-size: 1rem; font-weight: 600; margin: 20px 0 8px; color: var(--text);
}
.section p { margin-bottom: 14px; color: var(--text); font-size: .94rem; }
.section ul, .section ol {
  margin: 8px 0 16px 24px; font-size: .92rem;
}
.section li { margin-bottom: 6px; }

/* ===== PAGE TITLE (Hero) ===== */
.page-hero {
  padding: 40px 0 32px; margin-bottom: 20px;
  border-bottom: 1px solid var(--border);
}
.page-hero h1 { font-size: 2.2rem; font-weight: 700; margin-bottom: 8px; }
.page-hero h1 span { color: var(--accent); }
.page-hero p { font-size: 1.05rem; color: var(--text-muted); max-width: 680px; }
.page-hero .tags { display: flex; gap: 8px; margin-top: 12px; flex-wrap: wrap; }
.page-hero .tag {
  font-size: .72rem; padding: 3px 10px; border-radius: 20px;
  background: var(--tag-bg); color: var(--accent); font-weight: 500;
}

/* ===== CODE BLOCKS ===== */
.code-block {
  position: relative; background: var(--bg-code); border: 1px solid var(--border);
  border-radius: var(--radius); margin: 14px 0 22px; overflow: hidden;
}
.code-block .code-header {
  display: flex; justify-content: space-between; align-items: center;
  padding: 6px 16px; background: rgba(108,140,255,.05); border-bottom: 1px solid var(--border);
  font-size: .72rem; color: var(--text-muted); text-transform: uppercase; letter-spacing: .05em;
}
.code-block pre {
  padding: 18px 22px; overflow-x: auto; font-family: var(--font-code);
  font-size: .83rem; line-height: 1.75; color: var(--text);
}
.code-block .copy-btn {
  background: var(--bg-card); border: 1px solid var(--border); border-radius: 6px;
  padding: 3px 10px; font-size: .72rem; cursor: pointer; color: var(--text-muted);
  transition: all var(--transition);
}
.code-block .copy-btn:hover { border-color: var(--accent); color: var(--accent); }

/* Syntax highlighting */
.kw { color: #c678dd; }
.sel { color: #e06c75; }
.prop { color: #61afef; }
.val { color: #98c379; }
.cmt { color: #5c6370; font-style: italic; }
.fn { color: #e5c07b; }
.str { color: #98c379; }
.num { color: #d19a66; }
.unit { color: #56b6c2; }
.at { color: #c678dd; }
.tag { color: #e06c75; }
.attr { color: #d19a66; }

/* ===== LIVE EXAMPLE ===== */
.live-example {
  border: 1px solid var(--border); border-radius: var(--radius);
  padding: 24px; margin: 14px 0 22px; background: var(--bg-card);
}
.live-example-label {
  font-size: .72rem; text-transform: uppercase; letter-spacing: .06em;
  color: var(--text-muted); margin-bottom: 14px; font-weight: 600;
  display: flex; align-items: center; gap: 6px;
}
.live-example-label::before {
  content: ""; width: 8px; height: 8px; border-radius: 50%;
  background: var(--accent); display: inline-block;
}

/* ===== CALLOUT BOXES ===== */
.callout {
  border-radius: var(--radius); padding: 16px 20px; margin: 16px 0 22px;
  font-size: .88rem; border-left: 4px solid; line-height: 1.7;
}
.callout-title { font-weight: 600; margin-bottom: 6px; font-size: .88rem; }
.callout.gotcha { background: var(--gotcha-bg); border-color: var(--gotcha-border); }
.callout.gotcha .callout-title { color: var(--gotcha-border); }
.callout.tip { background: var(--tip-bg); border-color: var(--tip-border); }
.callout.tip .callout-title { color: var(--tip-border); }
.callout.info { background: var(--info-bg); border-color: var(--accent); }
.callout.info .callout-title { color: var(--accent); }

/* ===== TABLES ===== */
table {
  width: 100%; border-collapse: collapse; margin: 14px 0 22px; font-size: .87rem;
}
th, td { padding: 11px 16px; border: 1px solid var(--border); text-align: left; }
th {
  background: var(--bg-code); font-weight: 600; font-size: .8rem;
  text-transform: uppercase; letter-spacing: .04em;
}
tr:hover td { background: var(--hover-bg); }

/* ===== TOPIC NAV (Prev/Next) ===== */
.topic-nav {
  display: flex; justify-content: space-between; padding-top: 32px;
  border-top: 1px solid var(--border); margin-top: 48px; gap: 16px;
}
.topic-nav a {
  display: flex; flex-direction: column; padding: 16px 20px; border: 1px solid var(--border);
  border-radius: var(--radius); text-decoration: none; color: var(--text);
  transition: all var(--transition); flex: 1; max-width: 48%;
}
.topic-nav a:hover { border-color: var(--accent); background: var(--hover-bg); }
.topic-nav a .label { font-size: .72rem; color: var(--text-muted); text-transform: uppercase; letter-spacing: .05em; margin-bottom: 4px; }
.topic-nav a .title { font-weight: 600; font-size: .95rem; color: var(--accent); }
.topic-nav a.next { text-align: right; margin-left: auto; }

/* ===== LANDING PAGE ===== */
.landing-hero {
  text-align: center; padding: 80px 20px 60px;
}
.landing-hero h1 { font-size: 3rem; font-weight: 700; margin-bottom: 12px; }
.landing-hero h1 span { color: var(--accent); }
.landing-hero p { font-size: 1.15rem; color: var(--text-muted); max-width: 600px; margin: 0 auto 24px; }
.topics-grid {
  display: grid; grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 16px; padding: 0 40px 80px; max-width: 1200px; margin: 0 auto;
}
.topic-card {
  background: var(--bg-card); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 24px; text-decoration: none; color: var(--text); transition: all var(--transition);
  display: flex; flex-direction: column;
}
.topic-card:hover { border-color: var(--accent); transform: translateY(-2px); box-shadow: 0 2px 8px rgba(0,0,0,.1); }
.topic-card .num { font-size: .72rem; font-weight: 700; color: var(--accent); margin-bottom: 6px; }
.topic-card h3 { font-size: 1.05rem; font-weight: 600; margin-bottom: 6px; }
.topic-card p { font-size: .82rem; color: var(--text-muted); line-height: 1.5; }

/* ===== MOBILE ===== */
.menu-toggle {
  display: none; background: none; border: none; color: var(--text);
  font-size: 1.3rem; cursor: pointer; padding: 4px;
}

@media (max-width: 768px) {
  .sidebar { transform: translateX(-100%); }
  .sidebar.open { transform: translateX(0); }
  .main { margin-left: 0; padding: 24px 18px 60px; }
  .main.no-sidebar { padding: 20px 16px 60px; }
  .menu-toggle { display: block; }
  .header h1 { font-size: .95rem; }
  .header-nav { display: flex; gap: 4px; }
  .header-nav a { font-size: .72rem; padding: 4px 8px; }
  .landing-hero h1 { font-size: 2rem; }
  .landing-hero { padding: 50px 16px 40px; }
  .topics-grid { padding: 0 16px 60px; }
  .topic-nav { flex-direction: column; }
  .topic-nav a { max-width: 100%; }
  .page-hero h1 { font-size: 1.6rem; }
}
@media (min-width: 769px) and (max-width: 1024px) {
  .sidebar { width: 230px; }
  .main { margin-left: 230px; padding: 30px 30px 60px; }
}

/* ===== SCROLLBAR ===== */
/* Firefox */
html { scrollbar-width: thin; scrollbar-color: var(--scrollbar-thumb) transparent; }
/* Chrome / Safari / Edge */
::-webkit-scrollbar { width: 6px; height: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--scrollbar-thumb); border-radius: 3px; }

/* Utility */
.hidden { display: none !important; }
code {
  font-family: var(--font-code); background: var(--bg-code);
  padding: 2px 7px; border-radius: 4px; font-size: .84em;
}
strong { font-weight: 600; }

/* ===== FEATURE 1: GLOBAL SEARCH MODAL ===== */
.search-overlay {
  display: none; position: fixed; inset: 0; background: rgba(0,0,0,.55);
  z-index: 2000; align-items: flex-start; justify-content: center; padding-top: 12vh;
}
.search-overlay.open { display: flex; }
.search-modal {
  background: var(--bg-card); border: 1px solid var(--border); border-radius: 12px;
  width: 90%; max-width: 560px; box-shadow: 0 20px 60px rgba(0,0,0,.4);
  overflow: hidden; animation: searchSlideIn .15s ease;
}
@keyframes searchSlideIn { from { opacity: 0; transform: translateY(-12px); } to { opacity: 1; transform: translateY(0); } }
.search-input-wrap {
  display: flex; align-items: center; padding: 14px 18px; gap: 10px;
  border-bottom: 1px solid var(--border);
}
.search-input-wrap svg { width: 20px; height: 20px; color: var(--text-muted); flex-shrink: 0; }
.search-input {
  flex: 1; background: none; border: none; font-size: 1rem; color: var(--text);
  font-family: var(--font-body); outline: none;
}
.search-input::placeholder { color: var(--text-muted); }
.search-kbd {
  font-size: .68rem; padding: 2px 6px; border: 1px solid var(--border);
  border-radius: 4px; color: var(--text-muted); font-family: var(--font-code);
}
.search-results {
  max-height: 360px; overflow-y: auto; padding: 8px;
}
.search-results:empty::after {
  content: 'Type to search across all 21 topics...';
  display: block; text-align: center; padding: 32px; color: var(--text-muted); font-size: .88rem;
}
.search-result-item {
  display: block; padding: 10px 14px; border-radius: 8px; text-decoration: none;
  color: var(--text); margin-bottom: 2px; transition: background .1s;
}
.search-result-item:hover, .search-result-item.active {
  background: var(--hover-bg);
}
.search-result-item .sr-topic {
  font-size: .7rem; color: var(--accent); text-transform: uppercase;
  letter-spacing: .04em; font-weight: 600;
}
.search-result-item .sr-title {
  font-size: .9rem; font-weight: 600; margin-top: 2px;
}
.search-result-item .sr-snippet {
  font-size: .78rem; color: var(--text-muted); margin-top: 2px;
}
.search-result-item .sr-snippet mark {
  background: rgba(108,140,255,.25); color: var(--accent); border-radius: 2px;
  padding: 0 2px;
}
.search-no-results {
  text-align: center; padding: 32px; color: var(--text-muted); font-size: .88rem;
}
.search-trigger {
  background: none; border: 1px solid var(--border); border-radius: var(--radius);
  padding: 5px 12px; cursor: pointer; color: var(--text-muted); font-size: .8rem;
  transition: all var(--transition); display: flex; align-items: center; gap: 6px;
}
.search-trigger:hover { border-color: var(--accent); color: var(--accent); }

/* ===== FEATURE 4: SECTION DEEP LINKS ===== */
.section-anchor {
  opacity: 0; color: var(--accent); text-decoration: none; font-weight: 400;
  margin-left: 8px; transition: opacity .2s; font-size: .85em;
}
.section h2:hover .section-anchor,
.section h3:hover .section-anchor { opacity: 1; }

/* ===== FEATURE 5: BACK TO TOP BUTTON ===== */
.back-to-top {
  position: fixed; bottom: 32px; right: 32px; width: 44px; height: 44px;
  border-radius: 50%; background: var(--accent); color: #fff; border: none;
  cursor: pointer; font-size: 1.2rem; display: flex; align-items: center;
  justify-content: center; box-shadow: 0 2px 8px rgba(0,0,0,.15);
  transition: all .3s ease; opacity: 0; transform: translateY(20px);
  pointer-events: none; z-index: 998;
}
.back-to-top.visible { opacity: 1; transform: translateY(0); pointer-events: auto; }
.back-to-top:hover { transform: translateY(-3px); box-shadow: 0 4px 12px rgba(0,0,0,.2); }

/* ===== FEATURE 6: FONT SIZE CONTROLS ===== */
.font-size-controls {
  display: flex; align-items: center; gap: 2px; margin-left: 4px;
}
.font-size-controls button {
  background: none; border: 1px solid var(--border); border-radius: 4px;
  cursor: pointer; color: var(--text-muted); padding: 3px 8px;
  transition: all var(--transition); font-family: var(--font-body); font-weight: 600;
}
.font-size-controls button:hover { border-color: var(--accent); color: var(--accent); }
.font-size-controls button.active { background: var(--accent); color: #fff; border-color: var(--accent); }

/* ===== FEATURE 7: RELATED TOPICS ===== */
.related-topics {
  margin-top: 40px; padding-top: 24px; border-top: 1px solid var(--border);
}
.related-topics h3 {
  font-size: .82rem; text-transform: uppercase; letter-spacing: .06em;
  color: var(--text-muted); font-weight: 600; margin-bottom: 14px;
}
.related-grid {
  display: grid; grid-template-columns: repeat(auto-fit, minmax(200px, 1fr)); gap: 12px;
}
.related-card {
  background: var(--bg-card); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 16px; text-decoration: none; color: var(--text); transition: all var(--transition);
}
.related-card:hover { border-color: var(--accent); transform: translateY(-2px); box-shadow: 0 2px 8px rgba(0,0,0,.1); }
.related-card .rc-num { font-size: .68rem; color: var(--accent); font-weight: 700; }
.related-card .rc-title { font-size: .88rem; font-weight: 600; margin-top: 4px; }

/* ===== FEATURE 8: READING TIME ===== */
.reading-time {
  font-size: .82rem; color: var(--text-muted); margin-top: 10px;
  display: flex; align-items: center; gap: 6px;
}

/* ===== FEATURE 9: BROWSER SUPPORT BADGES ===== */
.browser-badge {
  display: inline-block; font-size: .66rem; padding: 2px 8px; border-radius: 10px;
  font-weight: 600; margin-left: 6px; vertical-align: middle;
}
.browser-badge.full { background: rgba(46,204,113,.15); color: #2ecc71; }
.browser-badge.partial { background: rgba(243,156,18,.15); color: #f39c12; }
.browser-badge.limited { background: rgba(231,76,60,.15); color: #e74c3c; }

/* ===== FEATURE 10: COLLAPSIBLE CODE BLOCKS ===== */
.code-block.collapsible pre {
  max-height: 280px; overflow: hidden; position: relative;
}
.code-block.collapsible.collapsed pre { max-height: 180px; }
.code-block.collapsible.collapsed pre::after {
  content: ''; position: absolute; bottom: 0; left: 0; right: 0; height: 60px;
  background: linear-gradient(transparent, var(--bg-code));
  pointer-events: none;
}
.code-expand-btn {
  display: block; width: 100%; padding: 6px; background: var(--bg-code);
  border: none; border-top: 1px solid var(--border); color: var(--accent);
  font-size: .78rem; cursor: pointer; font-family: var(--font-body);
  transition: background .2s;
}
.code-expand-btn:hover { background: var(--hover-bg); }

/* ===== FEATURE 3: TOPIC PROGRESS ON CARDS ===== */
.topic-card { position: relative; }
.topic-card .progress-check {
  position: absolute; top: 12px; right: 12px; width: 22px; height: 22px;
  border-radius: 50%; background: rgba(46,204,113,.15); color: #2ecc71;
  display: none; align-items: center; justify-content: center; font-size: .72rem;
}
.topic-card.visited .progress-check { display: flex; }
.landing-progress {
  text-align: center; font-size: .88rem; color: var(--text-muted); margin-bottom: 24px;
}
.landing-progress strong { color: var(--accent); }
.progress-bar-track {
  width: 200px; height: 6px; background: var(--border); border-radius: 3px;
  margin: 8px auto 0; overflow: hidden;
}
.progress-bar-fill {
  height: 100%; background: var(--accent);
  border-radius: 3px; transition: width .4s ease;
}

/* ===== FEATURE 11: KEYBOARD NAV TOAST ===== */
.kbd-toast {
  position: fixed; bottom: 24px; left: 50%; transform: translateX(-50%) translateY(80px);
  background: var(--bg-card); border: 1px solid var(--border); border-radius: 8px;
  padding: 10px 18px; font-size: .82rem; color: var(--text); z-index: 1500;
  box-shadow: 0 8px 32px rgba(0,0,0,.3); transition: transform .3s ease;
  display: flex; align-items: center; gap: 8px; white-space: nowrap;
}
.kbd-toast.visible { transform: translateX(-50%) translateY(0); }
.kbd-toast kbd {
  font-family: var(--font-code); font-size: .72rem; padding: 2px 6px;
  background: var(--bg-code); border: 1px solid var(--border); border-radius: 4px;
}

@media (max-width: 768px) {
  .search-trigger span { display: none; }
  .search-trigger .search-kbd { display: none; }
  .font-size-controls { display: none; }
  .back-to-top { bottom: 20px; right: 20px; width: 38px; height: 38px; font-size: 1rem; }
  .related-grid { grid-template-columns: 1fr; }
}

/* ===== SKIP LINK (Accessibility) ===== */
.skip-link {
  position: absolute; top: -100%; left: 16px;
  background: var(--accent); color: #fff; padding: 8px 16px;
  border-radius: var(--radius); font-size: .85rem; font-weight: 600;
  text-decoration: none; z-index: 2000;
  transition: top .2s ease;
}
.skip-link:focus {
  top: 8px;
}

/* ===== FOOTER ===== */
.site-footer {
  text-align: center; padding: 24px 16px;
  border-top: 1px solid var(--border);
  color: var(--text-muted); font-size: .8rem;
}

/* ===== PRINT STYLES ===== */
@media print {
  #progress, .header, .sidebar, .back-to-top, .search-overlay,
  .theme-toggle, .menu-toggle, .search-trigger, .font-size-controls,
  .kbd-toast, .topic-nav, .copy-btn, .code-expand-btn,
  .site-footer, .skip-link { display: none !important; }

  body { background: #fff; color: #000; font-size: 12pt; line-height: 1.6; }
  .main { margin-left: 0 !important; padding: 0 !important; max-width: 100% !important; }
  .main.no-sidebar { margin: 0 !important; padding: 0 !important; }
  .page-hero { padding: 0 0 12pt; }
  .section { margin-bottom: 24pt; }
  .code-block { border: 1px solid #ccc; break-inside: avoid; }
  .code-block pre { white-space: pre-wrap; word-wrap: break-word; }
  .live-example { border: 1px solid #ccc; break-inside: avoid; }
  .callout { break-inside: avoid; border-color: #999; }
  table { break-inside: avoid; }
  a { color: #000; text-decoration: underline; }
  a[href^="http"]::after { content: " (" attr(href) ")"; font-size: 9pt; color: #666; }
}