:root {
  --bg: #060910;
  --bg-2: #0a101c;
  --elev: #0d1526;
  --elev-2: #121c31;
  --line: rgba(146, 201, 255, 0.12);
  --line-strong: rgba(46, 233, 199, 0.35);
  --cyan: #2ee9c7;
  --cyan-dim: rgba(46, 233, 199, 0.12);
  --cyan-2: #7cf6e0;
  --blue: #4d8dff;
  --violet: #a78bfa;
  --amber: #f5b942;
  --rose: #fb7185;
  --text: #eef3ff;
  --muted: #9aa8c3;
  --faint: #6b7a96;
  --shadow: 0 18px 50px rgba(0, 0, 0, 0.35);
  --radius: 16px;
  --header-h: 68px;
  --font-sans: "Noto Sans TC", "Space Grotesk", ui-sans-serif, system-ui, sans-serif;
  --font-display: "Space Grotesk", "Noto Sans TC", ui-sans-serif, system-ui, sans-serif;
  --font-mono: "IBM Plex Mono", ui-monospace, monospace;
  --max: 1120px;
}

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

html {
  scroll-behavior: smooth;
  background: var(--bg);
}

html[lang="zh-Hant"] .display,
html[lang="zh-Hant"] h1,
html[lang="zh-Hant"] h2,
html[lang="zh-Hant"] h3 {
  font-family: "Noto Sans TC", sans-serif;
  letter-spacing: 0;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: var(--font-sans);
  color: var(--text);
  background: var(--bg);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

img { max-width: 100%; display: block; }
button, input { font: inherit; color: inherit; }
a { color: var(--cyan); text-decoration: none; }
a:hover { color: var(--cyan-2); }

.skip-link {
  position: absolute;
  left: 12px;
  top: -40px;
  background: var(--cyan);
  color: #04110d;
  padding: 8px 12px;
  z-index: 80;
  border-radius: 8px;
  font-weight: 700;
}
.skip-link:focus { top: 12px; }

.bg-grid {
  position: fixed;
  inset: 0;
  z-index: -2;
  background-image:
    linear-gradient(rgba(77, 141, 255, 0.05) 1px, transparent 1px),
    linear-gradient(90deg, rgba(77, 141, 255, 0.05) 1px, transparent 1px);
  background-size: 48px 48px;
  mask-image: radial-gradient(ellipse at 50% 0%, #000 20%, transparent 75%);
}

.bg-glow {
  position: fixed;
  inset: auto auto 10% -10%;
  width: 50vw;
  height: 50vw;
  z-index: -1;
  background: radial-gradient(circle, rgba(46, 233, 199, 0.12), transparent 60%);
  pointer-events: none;
}

/* Header */
.site-header {
  position: sticky;
  top: 0;
  z-index: 40;
  backdrop-filter: blur(16px);
  background: rgba(6, 9, 16, 0.78);
  border-bottom: 1px solid var(--line);
}

.header-inner {
  max-width: var(--max);
  margin: 0 auto;
  min-height: var(--header-h);
  padding: 0 20px;
  display: flex;
  align-items: center;
  gap: 24px;
}

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  color: var(--text);
}
.brand:hover { color: var(--text); }
.brand-text { display: flex; flex-direction: column; line-height: 1.15; }
.brand-text strong {
  font-family: var(--font-display);
  letter-spacing: 0.14em;
  font-size: 14px;
}
.brand-text span {
  font-size: 11px;
  color: var(--muted);
}

.nav-desktop {
  display: flex;
  gap: 6px;
  margin-left: auto;
}
.nav-desktop a,
.nav-mobile a {
  color: var(--muted);
  padding: 8px 12px;
  border-radius: 999px;
  font-size: 14px;
}
.nav-desktop a:hover,
.nav-mobile a:hover,
.nav-desktop a.active,
.nav-mobile a.active {
  color: var(--text);
  background: rgba(255, 255, 255, 0.05);
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-left: 8px;
}

.icon-btn {
  width: 38px;
  height: 38px;
  border: 1px solid var(--line);
  background: var(--elev);
  border-radius: 10px;
  color: var(--text);
  cursor: pointer;
  display: grid;
  place-items: center;
}
.icon-btn:hover { border-color: var(--line-strong); }

.lang-switch {
  display: flex;
  padding: 3px;
  background: var(--elev);
  border: 1px solid var(--line);
  border-radius: 999px;
}
.lang-switch button {
  border: 0;
  background: transparent;
  color: var(--muted);
  padding: 6px 10px;
  border-radius: 999px;
  cursor: pointer;
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.04em;
}
.lang-switch button.is-active {
  background: linear-gradient(135deg, var(--cyan), var(--blue));
  color: #04110d;
}

.hamburger {
  display: none;
  width: 38px;
  height: 38px;
  border: 1px solid var(--line);
  background: var(--elev);
  border-radius: 10px;
  cursor: pointer;
  padding: 9px 10px;
}
.hamburger span {
  display: block;
  height: 2px;
  background: var(--text);
  margin: 4px 0;
  border-radius: 2px;
}

.nav-mobile {
  display: flex;
  flex-direction: column;
  padding: 8px 16px 16px;
  border-top: 1px solid var(--line);
}
.nav-mobile[hidden] { display: none !important; }

.app {
  max-width: var(--max);
  margin: 0 auto;
  padding: 28px 20px 80px;
  min-height: calc(100vh - 220px);
}

/* Hero */
.hero {
  position: relative;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 28px;
  min-height: 420px;
  display: grid;
  align-items: end;
  background: #070b14 center/cover no-repeat;
  box-shadow: var(--shadow);
}
.hero::after {
  content: "";
  position: absolute;
  inset: 0;
  background:
    linear-gradient(180deg, rgba(6, 9, 16, 0.15) 0%, rgba(6, 9, 16, 0.55) 45%, rgba(6, 9, 16, 0.92) 100%),
    linear-gradient(90deg, rgba(6, 9, 16, 0.55), transparent 55%);
}
.hero-copy {
  position: relative;
  z-index: 1;
  padding: 36px;
  max-width: 680px;
}
.kicker {
  font-family: var(--font-mono);
  font-size: 12px;
  color: var(--cyan);
  letter-spacing: 0.08em;
  text-transform: uppercase;
  margin: 0 0 10px;
}
.display {
  font-family: var(--font-display);
  font-size: clamp(32px, 5vw, 52px);
  line-height: 1.12;
  margin: 0 0 14px;
  letter-spacing: -0.03em;
}
.lead { color: var(--muted); margin: 0 0 22px; font-size: 17px; }

.btn-row { display: flex; flex-wrap: wrap; gap: 10px; }
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  border-radius: 999px;
  padding: 11px 18px;
  border: 1px solid transparent;
  cursor: pointer;
  font-weight: 700;
  font-size: 14px;
}
.btn-primary {
  background: linear-gradient(135deg, var(--cyan), #1bb89c);
  color: #04110d;
}
.btn-primary:hover { color: #04110d; filter: brightness(1.08); }
.btn-ghost {
  background: rgba(255, 255, 255, 0.04);
  border-color: var(--line);
  color: var(--text);
}
.btn-ghost:hover { color: var(--text); border-color: var(--cyan); }

.stats {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
  margin: 18px 0 36px;
}
.stat {
  border: 1px solid var(--line);
  background: rgba(13, 21, 38, 0.8);
  border-radius: 16px;
  padding: 16px 18px;
}
.stat b {
  display: block;
  font-family: var(--font-display);
  font-size: 26px;
  color: var(--cyan);
}
.stat span { color: var(--muted); font-size: 13px; }

.section-head { margin: 8px 0 18px; }
.section-head h2 {
  font-family: var(--font-display);
  font-size: 28px;
  margin: 0 0 6px;
  letter-spacing: -0.03em;
}
.section-head p { margin: 0; color: var(--muted); }

/* Cards */
.topic-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 14px;
}
.topic-card {
  display: flex;
  flex-direction: column;
  gap: 10px;
  background: linear-gradient(180deg, var(--elev), #0b1322);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 18px;
  color: var(--text);
  min-height: 210px;
  transition: border-color .2s, transform .2s, box-shadow .2s;
  position: relative;
  overflow: hidden;
}
.topic-card:hover {
  color: var(--text);
  border-color: var(--line-strong);
  transform: translateY(-3px);
  box-shadow: 0 16px 40px rgba(46, 233, 199, 0.08);
}
.topic-card .num {
  font-family: var(--font-mono);
  font-size: 12px;
  color: var(--faint);
}
.topic-card h3 {
  margin: 0;
  font-size: 18px;
  line-height: 1.3;
}
.topic-card p {
  margin: 0;
  color: var(--muted);
  font-size: 14px;
  flex: 1;
}
.topic-card .meta {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 12px;
  color: var(--cyan);
}
.icon-pill {
  width: 38px;
  height: 38px;
  border-radius: 12px;
  display: grid;
  place-items: center;
  background: var(--cyan-dim, rgba(46, 233, 199, 0.12));
  color: var(--cyan);
  border: 1px solid rgba(46, 233, 199, 0.2);
}

.path {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(112px, 1fr));
  gap: 8px;
  margin-top: 16px;
}
.path a {
  background: var(--elev);
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 10px 8px;
  text-align: center;
  color: var(--text);
  font-size: 12px;
  min-height: 74px;
}
.path a:hover { border-color: var(--cyan); color: var(--text); }
.path a b { display: block; color: var(--cyan); font-family: var(--font-mono); margin-bottom: 4px; }

/* Topic page */
.crumb {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  color: var(--faint);
  font-size: 13px;
  margin-bottom: 16px;
}
.crumb a { color: var(--muted); }
.topic-hero {
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 18px;
  align-items: start;
  margin-bottom: 22px;
}
.topic-hero h1 {
  font-family: var(--font-display);
  font-size: clamp(28px, 4vw, 40px);
  margin: 0 0 8px;
  letter-spacing: -0.03em;
}
.topic-hero .lead { margin-bottom: 0; }
.score-chip {
  font-family: var(--font-mono);
  font-size: 12px;
  padding: 8px 12px;
  border-radius: 999px;
  border: 1px solid var(--line);
  color: var(--cyan);
  background: var(--elev);
}

.tabs {
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
  margin: 8px 0 18px;
  border-bottom: 1px solid var(--line);
  padding-bottom: 8px;
}
.tab {
  border: 0;
  background: transparent;
  color: var(--muted);
  padding: 8px 14px;
  border-radius: 999px;
  cursor: pointer;
}
.tab[aria-selected="true"] {
  background: rgba(46, 233, 199, 0.12);
  color: var(--cyan);
}
.panel[hidden] { display: none !important; }

.prose h3 { margin: 1.4em 0 .5em; font-size: 20px; }
.prose p { color: #d5deef; }
.prose ul, .prose ol { padding-left: 1.2em; color: #d5deef; }
.prose li { margin: 0.35em 0; }
.prose code, .mono {
  font-family: var(--font-mono);
  font-size: 0.92em;
  color: var(--cyan-2);
}

.callout {
  border: 1px solid var(--line);
  background: var(--elev);
  border-left: 3px solid var(--cyan);
  border-radius: 12px;
  padding: 14px 16px;
  margin: 16px 0;
}
.callout.warn { border-left-color: var(--amber); }
.callout.danger { border-left-color: var(--rose); }
.callout h4 { margin: 0 0 6px; font-size: 14px; }
.callout p { margin: 0; color: var(--muted); }

.table-wrap { overflow-x: auto; margin: 14px 0 22px; }
table {
  width: 100%;
  border-collapse: collapse;
  font-size: 14px;
}
th, td {
  text-align: left;
  padding: 10px 12px;
  border-bottom: 1px solid var(--line);
  vertical-align: top;
}
th { color: var(--cyan); font-weight: 600; font-size: 12px; letter-spacing: 0.04em; text-transform: uppercase; }
td { color: #d5deef; }

.accordion { display: grid; gap: 10px; }
.acc-item {
  border: 1px solid var(--line);
  background: var(--elev);
  border-radius: 14px;
  overflow: hidden;
}
.acc-item button {
  width: 100%;
  text-align: left;
  background: transparent;
  border: 0;
  color: var(--text);
  padding: 14px 16px;
  cursor: pointer;
  display: flex;
  justify-content: space-between;
  gap: 12px;
  font-weight: 700;
}
.acc-item button span.chev { color: var(--cyan); font-weight: 400; }
.acc-body { padding: 0 16px 14px; color: var(--muted); display: none; }
.acc-item.open .acc-body { display: block; }

.takeaways {
  display: grid;
  gap: 10px;
  margin: 18px 0;
}
.takeaways li {
  list-style: none;
  background: var(--elev);
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 12px 14px;
  color: #d5deef;
}
.takeaways { padding: 0; }

.related {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 10px;
  margin-top: 10px;
}
.related a {
  border: 1px solid var(--line);
  background: var(--elev);
  border-radius: 12px;
  padding: 12px;
  color: var(--text);
  font-size: 14px;
}
.related a:hover { border-color: var(--cyan); color: var(--text); }

/* Diagrams */
.diagram {
  border: 1px solid var(--line);
  background: radial-gradient(circle at 20% 0%, rgba(46, 233, 199, 0.08), transparent 40%), var(--elev);
  border-radius: 18px;
  padding: 16px;
}
.diagram h3 { margin: 0 0 12px; }
.diagram-help { color: var(--muted); font-size: 14px; margin: 0 0 12px; }
.diagram-detail {
  margin-top: 14px;
  padding: 12px;
  background: rgba(0, 0, 0, 0.22);
  border-radius: 12px;
  min-height: 96px;
  color: #d5deef;
}
.diagram-detail h4 { margin: 0 0 6px; color: var(--cyan); }

.osi {
  display: grid;
  gap: 6px;
}
.osi button {
  text-align: left;
  border: 1px solid var(--line);
  background: var(--elev-2);
  color: var(--text);
  padding: 10px 12px;
  border-radius: 10px;
  cursor: pointer;
  display: flex;
  justify-content: space-between;
  gap: 10px;
}
.osi button small { color: var(--faint); }
.osi button.active {
  border-color: var(--cyan);
  box-shadow: inset 0 0 0 1px var(--cyan);
}

.cia {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 10px;
}
.cia button {
  min-height: 110px;
  border-radius: 16px;
  border: 1px solid var(--line);
  background: var(--elev-2);
  color: var(--text);
  cursor: pointer;
  font-weight: 700;
}
.cia button.active { border-color: var(--cyan); color: var(--cyan); }

.rings {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}
.rings button {
  border-radius: 999px;
  border: 1px solid var(--line);
  background: transparent;
  color: var(--text);
  padding: 8px 12px;
  cursor: pointer;
}
.rings button.active { background: rgba(46, 233, 199, 0.12); border-color: var(--cyan); color: var(--cyan); }

.stepper-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 10px;
  margin-bottom: 12px;
}
.steps {
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
}
.steps span {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  background: #334155;
}
.steps span.on { background: var(--cyan); }

.kill {
  display: grid;
  grid-template-columns: repeat(7, 1fr);
  gap: 6px;
}
.kill button {
  border: 1px solid var(--line);
  background: var(--elev-2);
  color: var(--text);
  border-radius: 10px;
  padding: 10px 6px;
  cursor: pointer;
  font-size: 12px;
}
.kill button.active { border-color: var(--amber); color: var(--amber); }

.timeline {
  display: grid;
  gap: 10px;
}
.timeline button {
  text-align: left;
  border: 1px solid var(--line);
  background: var(--elev-2);
  color: var(--text);
  border-radius: 12px;
  padding: 12px;
  cursor: pointer;
}
.timeline button.active { border-color: var(--violet); }
.timeline button b { color: var(--violet); display: block; font-family: var(--font-mono); font-size: 12px; }

/* Quiz */
.quiz-card {
  border: 1px solid var(--line);
  background: var(--elev);
  border-radius: 18px;
  padding: 18px;
}
.quiz-q { font-size: 18px; margin: 0 0 14px; }
.options { display: grid; gap: 8px; }
.option {
  text-align: left;
  border: 1px solid var(--line);
  background: var(--elev-2);
  color: var(--text);
  padding: 12px 14px;
  border-radius: 12px;
  cursor: pointer;
}
.option.selected { border-color: var(--blue); }
.option.good { border-color: var(--cyan); background: rgba(46, 233, 199, 0.08); }
.option.bad { border-color: var(--rose); background: rgba(251, 113, 133, 0.08); }
.quiz-meta {
  display: flex;
  justify-content: space-between;
  color: var(--muted);
  font-size: 13px;
  margin-bottom: 10px;
  font-family: var(--font-mono);
}
.explain {
  margin-top: 12px;
  color: var(--muted);
  padding: 12px;
  background: rgba(0,0,0,.2);
  border-radius: 12px;
}
.quiz-actions { display: flex; gap: 8px; margin-top: 14px; flex-wrap: wrap; }
.progress-bar {
  height: 6px;
  background: #1e293b;
  border-radius: 999px;
  overflow: hidden;
  margin: 8px 0 16px;
}
.progress-bar span {
  display: block;
  height: 100%;
  background: linear-gradient(90deg, var(--cyan), var(--blue));
}

/* Glossary */
.glossary-list { display: grid; gap: 10px; }
.glossary-item {
  border: 1px solid var(--line);
  background: var(--elev);
  border-radius: 14px;
  padding: 14px 16px;
}
.glossary-item h3 { margin: 0 0 6px; font-size: 16px; }
.glossary-item p { margin: 0; color: var(--muted); }
.glossary-item .tag {
  font-family: var(--font-mono);
  font-size: 11px;
  color: var(--blue);
}

/* Search */
.search-overlay {
  position: fixed;
  inset: 0;
  background: rgba(2, 6, 12, 0.72);
  z-index: 60;
  display: grid;
  place-items: start center;
  padding: 12vh 16px 16px;
}
.search-overlay[hidden] { display: none !important; }
.search-panel {
  width: min(720px, 100%);
  background: #0d1526;
  border: 1px solid var(--line);
  border-radius: 18px;
  padding: 16px;
  box-shadow: var(--shadow);
}
.search-head { display: flex; justify-content: space-between; align-items: center; }
.search-head h2 { margin: 0; font-size: 16px; }
.search-panel input {
  width: 100%;
  margin: 12px 0;
  background: #070b14;
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 12px 14px;
  outline: none;
}
.search-panel input:focus { border-color: var(--cyan); }
.search-results a {
  display: block;
  padding: 10px 8px;
  border-radius: 10px;
  color: var(--text);
}
.search-results a:hover { background: rgba(255,255,255,0.04); }
.search-results small { color: var(--muted); display: block; }

/* Footer */
.site-footer {
  border-top: 1px solid var(--line);
  background: #070b14;
  padding: 32px 20px 20px;
}
.footer-inner {
  max-width: var(--max);
  margin: 0 auto 18px;
  display: grid;
  grid-template-columns: 1.4fr 0.6fr 1.2fr;
  gap: 24px;
}
.footer-inner p { color: var(--muted); margin: 8px 0 0; font-size: 14px; }
.footer-inner a { display: block; color: var(--muted); margin: 6px 0; }
.footer-label {
  font-size: 12px !important;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--faint) !important;
  margin: 0 !important;
}
.copyright {
  max-width: var(--max);
  margin: 0 auto;
  color: var(--faint);
  font-size: 12px;
}

.noscript {
  padding: 20px;
  text-align: center;
  color: var(--amber);
}

.source-list { padding-left: 1.1em; }
.source-list a { color: var(--blue); }

.about-grid {
  display: grid;
  grid-template-columns: 1.2fr 0.8fr;
  gap: 16px;
}
.card-plain {
  border: 1px solid var(--line);
  background: var(--elev);
  border-radius: 16px;
  padding: 18px;
}

@media (max-width: 980px) {
  .topic-grid, .related, .stats, .cia, .kill { grid-template-columns: repeat(2, 1fr); }
  .path { grid-template-columns: repeat(3, 1fr); }
  .footer-inner, .about-grid, .topic-hero { grid-template-columns: 1fr; }
}

@media (max-width: 760px) {
  .nav-desktop { display: none; }
  .hamburger { display: block; }
  .stats, .topic-grid, .related, .cia, .kill { grid-template-columns: 1fr; }
  .hero-copy { padding: 24px 18px; }
  .header-inner { gap: 10px; }
  .brand-text span { display: none; }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  .topic-card { transition: none; }
}

:focus-visible {
  outline: 2px solid var(--cyan);
  outline-offset: 2px;
}

::selection {
  background: rgba(46, 233, 199, 0.28);
  color: #fff;
}