:root {
  --bg: #f5f7fb;
  --panel: #ffffff;
  --text: #1d2a3b;
  --muted: #5f6f84;
  --line: #dbe3ef;
  --primary: #2a66c9;
  --primary-soft: #e8f0ff;
  --shadow: 0 10px 25px rgba(17, 38, 76, 0.08);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: "Segoe UI", "PingFang SC", "Hiragino Sans GB", sans-serif;
  color: var(--text);
  background:
    radial-gradient(circle at 10% 0%, #eef4ff 0%, transparent 35%),
    radial-gradient(circle at 90% 10%, #ecf3ff 0%, transparent 32%),
    var(--bg);
  line-height: 1.6;
}

.topbar {
  position: sticky;
  top: 0;
  z-index: 20;
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
  padding: 0.9rem 1.2rem;
  border-bottom: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.92);
  backdrop-filter: blur(8px);
}

.brand {
  display: flex;
  gap: 0.7rem;
  align-items: center;
}

.dot {
  width: 13px;
  height: 13px;
  border-radius: 50%;
  background: linear-gradient(135deg, #80b0ff, #2a66c9);
}

.brand-cn,
.brand-en {
  margin: 0;
}

.brand-cn {
  font-size: 0.95rem;
  font-weight: 700;
}

.brand-en {
  font-size: 0.75rem;
  color: var(--muted);
}

.topnav {
  display: flex;
  gap: 0.8rem;
  flex-wrap: wrap;
  justify-content: flex-end;
}

.topnav a {
  text-decoration: none;
  color: var(--muted);
  padding: 0.28rem 0.45rem;
  border-radius: 8px;
  font-size: 0.9rem;
}

.topnav a:hover {
  color: var(--primary);
  background: var(--primary-soft);
}

.topnav a.active {
  color: var(--primary);
  background: var(--primary-soft);
  font-weight: 600;
}

.layout {
  max-width: 980px;
  margin: 1.2rem auto;
  padding: 0 1rem 1.5rem;
}

.layout.with-sidebar {
  max-width: 1180px;
  display: grid;
  grid-template-columns: 280px 1fr;
  gap: 1rem;
  align-items: start;
}

.content {
  display: grid;
  gap: 1rem;
}

.card {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 14px;
  box-shadow: var(--shadow);
  padding: 1.1rem;
}

.hero h1 {
  margin: 0.2rem 0 0.5rem;
  font-size: 1.65rem;
}

.tag {
  margin: 0;
  display: inline-block;
  padding: 0.2rem 0.55rem;
  border-radius: 999px;
  background: var(--primary-soft);
  color: var(--primary);
  font-size: 0.82rem;
  font-weight: 600;
}

.grid {
  display: grid;
  gap: 0.75rem;
}

.grid.two {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.grid.three {
  grid-template-columns: repeat(3, minmax(0, 1fr));
}

.grid article {
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 0.75rem;
  background: #fdfefe;
}

.cards {
  display: grid;
  gap: 1rem;
}

.module-grid {
  display: grid;
  gap: 0.9rem;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
}

.module-card {
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 0.9rem;
  background: #fdfefe;
}

.module-card p {
  margin: 0;
  color: var(--muted);
  line-height: 1.7;
}



li {
  line-height: 1.7;
}

.anchor {
  scroll-margin-top: 92px;
}

.page-nav {
  padding-top: 0.9rem;
  padding-bottom: 0.9rem;
}

.page-nav h2 {
  font-size: 1rem;
  margin-bottom: 0.55rem;
}

.page-nav-list {
  list-style: none;
  padding: 0;
  margin: 0;
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
}

.page-nav-list a {
  display: inline-block;
  text-decoration: none;
  font-size: 0.88rem;
  color: var(--muted);
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 0.22rem 0.65rem;
  background: #fdfefe;
}

.page-nav-list a:hover {
  color: var(--primary);
  border-color: #bfd2f7;
  background: var(--primary-soft);
}

.page-nav-list a.is-current,
.toc a.is-current {
  color: var(--primary);
  border-color: #9dbcf2;
  background: var(--primary-soft);
  font-weight: 600;
}

.sidebar {
  position: sticky;
  top: 86px;
}

.toc {
  list-style: none;
  padding: 0;
  margin: 0.75rem 0 0;
  display: grid;
  gap: 0.35rem;
}

.toc a {
  display: block;
  text-decoration: none;
  color: var(--muted);
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 0.45rem 0.55rem;
  background: #fdfefe;
  font-size: 0.9rem;
}

.toc a:hover {
  color: var(--primary);
  border-color: #bfd2f7;
  background: var(--primary-soft);
}

h2 {
  margin-top: 0;
  font-size: 1.25rem;
}

h3 {
  margin: 0 0 0.3rem;
  font-size: 1rem;
}

ul {
  margin: 0;
  padding-left: 1.2rem;
}

.formula p {
  margin: 0;
  font-family: "Consolas", "Cascadia Mono", monospace;
  font-size: 0.92rem;
  color: #2f3f56;
}

@media (max-width: 980px) {
  .topbar {
    align-items: flex-start;
    flex-direction: column;
  }

  .topnav {
    justify-content: flex-start;
  }

  .grid.two,
  .grid.three {
    grid-template-columns: 1fr;
  }

  .layout.with-sidebar {
    grid-template-columns: 1fr;
  }

  .sidebar {
    position: static;
  }
}