:root {
  --bg: #ffffff;
  --bg-soft: #f6f7f9;
  --card: #ffffff;
  --text: #1d2025;
  --text-soft: #555b66;
  --muted: #8a909b;
  --brand: #3b5bdb;
  --brand-soft: #edf0fd;
  --border: #e6e8ec;
  --radius: 14px;
  --maxw: 760px;
  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue",
    "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0e0f12;
    --bg-soft: #15171c;
    --card: #16181d;
    --text: #e9ebf0;
    --text-soft: #b6bcc6;
    --muted: #7e8593;
    --brand: #7891ff;
    --brand-soft: #1d2236;
    --border: #262a31;
  }
}

* { box-sizing: border-box; }

html { -webkit-text-size-adjust: 100%; }

body {
  margin: 0;
  font-family: var(--font);
  background: var(--bg-soft);
  color: var(--text);
  line-height: 1.7;
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
}

.wrap {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 24px 20px 64px;
}

/* Top bar */
.topbar {
  position: sticky;
  top: 0;
  z-index: 10;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 12px 20px;
  background: color-mix(in srgb, var(--bg) 88%, transparent);
  backdrop-filter: saturate(160%) blur(12px);
  -webkit-backdrop-filter: saturate(160%) blur(12px);
  border-bottom: 1px solid var(--border);
}

.topbar .home {
  display: flex;
  align-items: center;
  gap: 10px;
  text-decoration: none;
  color: var(--text);
  font-weight: 700;
  font-size: 17px;
}

.logo {
  width: 30px;
  height: 30px;
  border-radius: 8px;
  background: linear-gradient(135deg, var(--brand), #6f86ff);
  color: #fff;
  display: grid;
  place-items: center;
  font-weight: 800;
  font-size: 15px;
  flex: 0 0 auto;
}

/* Language switch */
.lang-switch {
  display: inline-flex;
  border: 1px solid var(--border);
  border-radius: 999px;
  overflow: hidden;
  background: var(--card);
}

.lang-switch button {
  appearance: none;
  border: 0;
  background: transparent;
  color: var(--text-soft);
  font: inherit;
  font-size: 14px;
  padding: 6px 14px;
  cursor: pointer;
  transition: background .15s, color .15s;
}

.lang-switch button.active {
  background: var(--brand);
  color: #fff;
}

/* Hero (landing) */
.hero {
  text-align: center;
  padding: 48px 16px 24px;
}

.hero .logo-lg {
  width: 76px;
  height: 76px;
  border-radius: 18px;
  margin: 0 auto 18px;
  font-size: 34px;
}

.hero h1 {
  font-size: 30px;
  margin: 0 0 8px;
  letter-spacing: -0.5px;
}

.hero .tagline {
  color: var(--text-soft);
  font-size: 16px;
  margin: 0 auto;
  max-width: 460px;
}

.badges {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  justify-content: center;
  margin: 22px 0 4px;
}

.badge {
  font-size: 13px;
  color: var(--brand);
  background: var(--brand-soft);
  border: 1px solid color-mix(in srgb, var(--brand) 25%, transparent);
  padding: 5px 12px;
  border-radius: 999px;
}

/* Cards / nav links */
.cards {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 14px;
  margin-top: 28px;
}

@media (max-width: 560px) {
  .cards { grid-template-columns: 1fr; }
}

.card-link {
  display: block;
  text-decoration: none;
  color: var(--text);
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px;
  transition: transform .15s, border-color .15s, box-shadow .15s;
}

.card-link:hover {
  transform: translateY(-2px);
  border-color: color-mix(in srgb, var(--brand) 40%, var(--border));
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.06);
}

.card-link .ic { font-size: 24px; }
.card-link h3 { margin: 10px 0 4px; font-size: 18px; }
.card-link p { margin: 0; color: var(--text-soft); font-size: 14px; }

/* Document */
.doc {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 28px 26px;
  margin-top: 18px;
}

@media (max-width: 560px) {
  .doc { padding: 22px 18px; }
}

.doc h1 {
  font-size: 26px;
  margin: 0 0 4px;
  letter-spacing: -0.4px;
}

.doc .eff {
  color: var(--muted);
  font-size: 14px;
  margin: 0 0 20px;
}

.doc h2 {
  font-size: 19px;
  margin: 28px 0 8px;
  padding-top: 4px;
}

.doc h2:first-of-type { margin-top: 8px; }

.doc p, .doc li { color: var(--text-soft); }
.doc strong { color: var(--text); }

.doc ul { padding-left: 20px; margin: 8px 0; }
.doc li { margin: 4px 0; }

.callout {
  background: var(--brand-soft);
  border: 1px solid color-mix(in srgb, var(--brand) 22%, transparent);
  border-radius: 12px;
  padding: 14px 16px;
  margin: 18px 0;
  color: var(--text);
  font-size: 15px;
}

.callout strong { color: var(--brand); }

a.inline { color: var(--brand); text-decoration: none; }
a.inline:hover { text-decoration: underline; }

.footer {
  text-align: center;
  color: var(--muted);
  font-size: 13px;
  margin-top: 40px;
}

.footer a { color: var(--muted); }

.back {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  margin-top: 24px;
  text-decoration: none;
  color: var(--brand);
  font-size: 15px;
}

/* Language visibility */
[data-lang] { display: none; }
html[lang="zh"] [data-lang="zh"] { display: revert; }
html[lang="en"] [data-lang="en"] { display: revert; }
/* block-level wrappers */
html[lang="zh"] section[data-lang="zh"],
html[lang="en"] section[data-lang="en"] { display: block; }