:root {
  --bg: #f3f8ff;
  --panel: #ffffff;
  --panel-soft: linear-gradient(180deg, #f8fbff 0%, #eef6ff 100%);
  --line: #d7e6fb;
  --text: #15304d;
  --muted: #587190;
  --brand: #1f78d1;
  --brand-strong: #0f5eb3;
  --shadow: 0 18px 40px rgba(31, 120, 209, 0.12);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  background:
    radial-gradient(circle at top left, rgba(111, 185, 255, 0.22), transparent 32%),
    linear-gradient(180deg, #f6fbff 0%, #edf5ff 100%);
  color: var(--text);
  font: 15px/1.7 "Segoe UI", "PingFang SC", "Noto Sans SC", "Microsoft YaHei", sans-serif;
}
a { color: var(--brand-strong); text-decoration: none; }
a:hover { text-decoration: underline; }
code {
  background: #eaf3ff;
  color: #0f5eb3;
  padding: 0.12rem 0.38rem;
  border-radius: 0.42rem;
  font-family: "SFMono-Regular", Consolas, monospace;
  font-size: 0.93em;
}
.layout {
  min-height: 100vh;
  display: grid;
  grid-template-columns: 280px minmax(0, 1fr);
}
.sidebar {
  position: sticky;
  top: 0;
  align-self: start;
  height: 100vh;
  overflow-y: auto;
  padding: 1.5rem 1.2rem 2rem;
  border-right: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.76);
  backdrop-filter: blur(16px);
}
.brand {
  display: block;
  padding: 0.95rem 1rem;
  border: 1px solid var(--line);
  border-radius: 1rem;
  background: var(--panel-soft);
  box-shadow: var(--shadow);
  color: var(--text);
}
.brand:hover { text-decoration: none; }
.brand-kicker {
  display: block;
  margin-bottom: 0.2rem;
  font-size: 0.75rem;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--brand);
}
.nav-group { margin-top: 1.5rem; }
.nav-group h2 {
  margin: 0 0 0.65rem;
  font-size: 0.8rem;
  letter-spacing: 0.08em;
  color: var(--muted);
}
.nav-group ul {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: 0.35rem;
}
.nav-group a {
  display: block;
  padding: 0.7rem 0.85rem;
  border-radius: 0.85rem;
  color: var(--text);
}
.nav-group a:hover {
  background: rgba(31, 120, 209, 0.08);
  text-decoration: none;
}
.nav-group a.active {
  background: linear-gradient(135deg, #1f78d1 0%, #5aa0ea 100%);
  color: #fff;
  box-shadow: 0 14px 30px rgba(31, 120, 209, 0.22);
}
.content-wrap {
  padding: 2rem clamp(1rem, 3vw, 2.4rem) 3rem;
}
.hero {
  padding: 1.6rem clamp(1.1rem, 2vw, 1.8rem);
  border: 1px solid var(--line);
  border-radius: 1.4rem;
  background: var(--panel-soft);
  box-shadow: var(--shadow);
}
.hero-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
}
.eyebrow {
  margin: 0 0 0.3rem;
  font-size: 0.78rem;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--brand);
}
.language-switch {
  display: flex;
  align-items: center;
  gap: 0.8rem;
  font-size: 0.92rem;
}
.language-switch .current {
  font-weight: 700;
  color: var(--text);
}
.hero h1 {
  margin: 0;
  font-size: clamp(1.7rem, 4vw, 2.5rem);
  line-height: 1.2;
}
.content-grid {
  margin-top: 1.25rem;
  display: grid;
  grid-template-columns: minmax(0, 1fr) 250px;
  gap: 1.25rem;
  align-items: start;
}
.content {
  min-width: 0;
  padding: 1.6rem clamp(1.1rem, 2vw, 1.8rem);
  border: 1px solid var(--line);
  border-radius: 1.35rem;
  background: var(--panel);
  box-shadow: var(--shadow);
}
.toc {
  position: sticky;
  top: 1.2rem;
}
.toc-card {
  padding: 1rem;
  border: 1px solid var(--line);
  border-radius: 1.1rem;
  background: rgba(255,255,255,0.88);
  box-shadow: var(--shadow);
}
.toc-title {
  margin: 0 0 0.7rem;
  font-size: 0.8rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--muted);
}
.toc ul { list-style: none; margin: 0; padding: 0; display: grid; gap: 0.45rem; }
.toc li.level-3 { padding-left: 0.8rem; }
.toc a { color: var(--muted); }
.toc a:hover { color: var(--brand-strong); }
.prose h1, .prose h2, .prose h3 { line-height: 1.3; scroll-margin-top: 1rem; }
.prose h1 { margin: 0 0 1rem; font-size: 2rem; }
.prose h2 {
  margin: 2rem 0 0.8rem;
  padding-top: 0.2rem;
  font-size: 1.32rem;
  border-top: 1px solid #edf3fb;
}
.prose h3 { margin: 1.4rem 0 0.6rem; font-size: 1.05rem; }
.prose p { margin: 0.7rem 0; }
.prose ul, .prose ol { margin: 0.7rem 0 0.9rem 1.2rem; padding: 0; }
.prose li + li { margin-top: 0.35rem; }

@media (max-width: 1100px) {
  .content-grid {
    grid-template-columns: 1fr;
  }
  .toc {
    position: static;
  }
}

@media (max-width: 860px) {
  .layout {
    grid-template-columns: 1fr;
  }
  .sidebar {
    position: static;
    height: auto;
    border-right: 0;
    border-bottom: 1px solid var(--line);
  }
  .hero-head {
    flex-direction: column;
    align-items: flex-start;
  }
}