:root {
  --bg: #f3f5fb;
  --surface: rgba(255, 255, 255, 0.76);
  --surface-solid: #ffffff;
  --text: #172033;
  --muted: #5a6477;
  --primary: #3b82f6;
  --primary-strong: #2563eb;
  --accent: #8b5cf6;
  --border: rgba(23, 32, 51, 0.12);
  --shadow-soft: 0 12px 34px rgba(18, 39, 77, 0.12);
  --shadow-card: 0 8px 20px rgba(18, 39, 77, 0.08);
  --radius-lg: 20px;
  --radius-md: 14px;
  --radius-sm: 10px;
  --gradient: linear-gradient(130deg, #3b82f6 0%, #7c3aed 55%, #06b6d4 100%);
}

body[data-theme="dark"] {
  --bg: #0e1222;
  --surface: rgba(16, 22, 40, 0.74);
  --surface-solid: #141b30;
  --text: #eef3ff;
  --muted: #a6b0ca;
  --primary: #60a5fa;
  --primary-strong: #3b82f6;
  --accent: #c084fc;
  --border: rgba(161, 178, 220, 0.2);
  --shadow-soft: 0 20px 38px rgba(0, 0, 0, 0.4);
  --shadow-card: 0 10px 20px rgba(0, 0, 0, 0.3);
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  font-family: "Inter", "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  background: radial-gradient(circle at 10% 0%, rgba(59,130,246,0.18), transparent 38%),
    radial-gradient(circle at 90% 10%, rgba(139,92,246,0.18), transparent 42%),
    var(--bg);
  color: var(--text);
  line-height: 1.6;
  transition: background-color 0.3s ease, color 0.3s ease;
}

a { color: inherit; text-decoration: none; }

img { max-width: 100%; display: block; }

.container {
  width: min(1120px, calc(100% - 2rem));
  margin: 0 auto;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 30;
  backdrop-filter: blur(12px);
  background: color-mix(in srgb, var(--surface) 90%, transparent);
  border-bottom: 1px solid var(--border);
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.9rem 0;
  gap: 0.9rem;
  flex-wrap: wrap;
}

.brand {
  font-size: 1.15rem;
  font-weight: 700;
  letter-spacing: -0.02em;
}

.brand span {
  background: var(--gradient);
  -webkit-background-clip: text;
  color: transparent;
}

.nav-links {
  display: flex;
  gap: 0.45rem;
  flex-wrap: wrap;
}

.nav-links a {
  padding: 0.5rem 0.75rem;
  border-radius: 999px;
  color: var(--muted);
  font-weight: 500;
  font-size: 0.92rem;
  transition: 0.2s ease;
}

.nav-links a[aria-current="page"],
.nav-links a:hover {
  color: var(--text);
  background: color-mix(in srgb, var(--primary) 14%, transparent);
}

.controls {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  margin-left: auto;
}

.search-wrap {
  display: flex;
  align-items: center;
  gap: 0.35rem;
  background: var(--surface-solid);
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 0.35rem 0.75rem;
  box-shadow: var(--shadow-card);
}

.search-wrap input {
  border: none;
  outline: none;
  background: transparent;
  color: var(--text);
  width: 180px;
  font-size: 0.9rem;
}

.search-wrap button,
.theme-toggle,
.btn {
  border: none;
  border-radius: 999px;
  padding: 0.5rem 0.9rem;
  background: var(--gradient);
  color: white;
  font-weight: 600;
  cursor: pointer;
  transition: transform 0.2s ease, box-shadow 0.2s ease;
  box-shadow: var(--shadow-card);
}

.search-wrap button:hover,
.theme-toggle:hover,
.btn:hover {
  transform: translateY(-1px);
}

.theme-toggle {
  background: var(--surface-solid);
  color: var(--text);
  border: 1px solid var(--border);
}

.hero {
  margin-top: 1.4rem;
  padding: 2.2rem 1.2rem;
  border-radius: var(--radius-lg);
  position: relative;
  overflow: hidden;
  background: linear-gradient(130deg, rgba(59,130,246,0.2), rgba(139,92,246,0.18)), var(--surface);
  border: 1px solid var(--border);
  box-shadow: var(--shadow-soft);
}

.glass-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  backdrop-filter: blur(12px);
  box-shadow: var(--shadow-card);
}

.hero h1 {
  margin: 0;
  line-height: 1.15;
  font-size: clamp(1.7rem, 4vw, 2.8rem);
}

.hero p {
  margin: 0.9rem 0 1.2rem;
  color: var(--muted);
  max-width: 64ch;
}

.hero-grid {
  display: grid;
  gap: 1rem;
  margin-top: 1.3rem;
}

.section {
  margin: 2rem 0;
}

.section h2 {
  font-size: clamp(1.3rem, 2.8vw, 1.8rem);
  margin-bottom: 0.35rem;
}

.section-intro {
  color: var(--muted);
  margin-top: 0;
}

.card-grid {
  display: grid;
  gap: 1rem;
}

.card {
  padding: 1rem;
}

.card h3 {
  margin-top: 0;
  margin-bottom: 0.35rem;
  font-size: 1.05rem;
}

.card p {
  margin: 0;
  color: var(--muted);
}

.tag {
  display: inline-flex;
  border-radius: 999px;
  background: color-mix(in srgb, var(--primary) 16%, transparent);
  color: var(--primary-strong);
  font-size: 0.76rem;
  font-weight: 600;
  padding: 0.22rem 0.6rem;
  margin-bottom: 0.65rem;
}

.math-box {
  margin-top: 0.9rem;
  padding: 0.7rem;
  border-radius: var(--radius-sm);
  background: color-mix(in srgb, var(--surface-solid) 84%, transparent);
  border: 1px solid var(--border);
  overflow-x: auto;
}

.table-wrap { overflow-x: auto; }

table {
  width: 100%;
  border-collapse: collapse;
  border-radius: var(--radius-sm);
  overflow: hidden;
  border: 1px solid var(--border);
}

th,
td {
  padding: 0.7rem;
  border-bottom: 1px solid var(--border);
  text-align: left;
  vertical-align: top;
}

th {
  background: color-mix(in srgb, var(--primary) 15%, transparent);
}

.search-host {
  position: relative;
}

.search-results {
  position: absolute;
  top: 100%;
  left: 0;
  right: 0;
  margin-top: 0.5rem;
  padding: 0.6rem;
  display: none;
  z-index: 1000;
  max-height: 300px;
  overflow-y: auto;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-soft);
}

.search-results.active { display: block; }

.search-results ul {
  margin: 0;
  padding: 0;
  list-style: none;
  display: grid;
  gap: 0.5rem;
}

.search-results a {
  display: block;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 0.55rem;
  background: var(--surface-solid);
}

.search-results small {
  color: var(--muted);
}

.footer {
  margin-top: 2.4rem;
  padding: 0.9rem 0 1.1rem;
  width: 100%;
  background: var(--surface-solid);
  border-top: 1px solid var(--border);
  color: var(--muted);
}

@media (min-width: 720px) {
  .hero-grid {
    grid-template-columns: repeat(3, minmax(0, 1fr));
  }

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

@media (min-width: 940px) {
  .card-grid.triple {
    grid-template-columns: repeat(3, minmax(0, 1fr));
  }
}

.toc {
  padding: 1rem;
}

.toc ul {
  margin: 0;
  padding-left: 1.1rem;
}

.toc li { margin: 0.35rem 0; }

.content-block {
  padding: 1.1rem;
  margin-top: 0.9rem;
}

.content-block h3,
.content-block h4 {
  margin: 0.3rem 0 0.5rem;
}

.content-block p,
.content-block li {
  color: var(--muted);
}

.content-block ul,
.content-block ol {
  margin: 0.45rem 0 0;
  padding-left: 1.2rem;
}

.footer-panel {
  padding: 1.1rem 0;
}

.footer-grid {
  display: grid;
  gap: 1rem;
}

.footer-grid h3,
.footer-grid h4 {
  margin: 0 0 0.4rem;
}

.footer-grid p,
.footer-grid li,
.footer-copy {
  color: var(--muted);
}

.footer-grid ul {
  margin: 0;
  padding-left: 1.1rem;
}

.footer-copy {
  margin: 0.9rem 0 0;
  padding-top: 0.7rem;
  border-top: 1px solid var(--border);
  text-align: center;
}

.media-links {
  margin: 0;
  padding-left: 1.1rem;
}

.media-links a {
  color: var(--primary-strong);
}


.course-grid {
  display: grid;
  gap: 0.8rem;
}

.course-item {
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 0.7rem;
  background: color-mix(in srgb, var(--surface-solid) 85%, transparent);
}

@media (min-width: 860px) {
  .footer-grid {
    grid-template-columns: 1.4fr repeat(3, 1fr);
  }

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

.course-link {
  display: block;
  transition: transform 0.2s ease, border-color 0.2s ease;
}

.course-link:hover {
  transform: translateY(-2px);
  border-color: color-mix(in srgb, var(--primary) 35%, var(--border));
}

.course-filter {
  display: flex;
  flex-wrap: wrap;
  gap: 0.55rem;
  margin: 0.9rem 0 0.6rem;
}

.course-filter-btn {
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 0.4rem 0.85rem;
  background: var(--surface-solid);
  color: var(--text);
  font-weight: 600;
  cursor: pointer;
}

.course-filter-btn.active {
  background: var(--gradient);
  color: #fff;
  border-color: transparent;
}

.filter-status {
  color: var(--muted);
  font-size: 0.92rem;
  margin-bottom: 0.8rem;
}

.theorem-card {
  display: block;
}

.theorem-card[hidden] {
  display: none;
}

.theorem-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  margin-top: 0.75rem;
}

.hash-tag {
  display: inline-flex;
  align-items: center;
  padding: 0.2rem 0.55rem;
  border-radius: 999px;
  border: 1px solid var(--border);
  background: color-mix(in srgb, var(--surface-solid) 88%, transparent);
  color: var(--muted);
  font-size: 0.78rem;
  font-weight: 600;
}

.hash-tag-course {
  color: var(--primary-strong);
}