*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

:root {
  --color-primary: #18181b;
  --color-secondary: #3f3f46;
  --color-accent: #2563eb;
  --color-bg: #fafafa;
  --color-text: #09090b;
  --color-muted: #71717a;
  --color-border: #e4e4e7;
  --color-surface: #ffffff;
  --font-serif: "Crimson Pro", "Noto Serif SC", Georgia, serif;
  --font-sans: "Atkinson Hyperlegible", "Noto Sans SC", system-ui, sans-serif;
  --font-mono: "SF Mono", "Fira Code", "JetBrains Mono", Consolas, monospace;
  --max-width: 1200px;
  --content-width: 820px;
  --radius-card: 14px;
  --shadow-soft: 0 14px 30px rgba(9, 9, 11, 0.045);
}

html {
  font-size: 17px;
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-sans);
  color: var(--color-text);
  background:
    linear-gradient(180deg, rgba(37, 99, 235, 0.03), transparent 180px),
    var(--color-bg);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

a {
  color: var(--color-accent);
  text-decoration: none;
  border-bottom: 1px solid transparent;
  transition: color 0.2s ease, border-color 0.2s ease, transform 0.2s ease;
}

a:hover,
a:focus-visible {
  border-bottom-color: var(--color-accent);
}

a:focus-visible {
  outline: 2px solid rgba(37, 99, 235, 0.35);
  outline-offset: 3px;
}

.site-header {
  display: grid;
  justify-items: center;
  border-bottom: 1px solid var(--color-border);
  padding: 2.4rem 1.5rem 2rem;
  text-align: center;
}

.site-header h1 {
  font-family: var(--font-serif);
  font-size: 2.65rem;
  font-weight: 700;
  letter-spacing: -0.025em;
  line-height: 1.08;
  color: var(--color-primary);
  margin-bottom: 0.4rem;
}

.site-header h1 span {
  display: block;
  margin-top: 0.42rem;
  font-family: var(--font-sans);
  font-size: 0.38em;
  font-weight: 700;
  letter-spacing: 0.04em;
  color: var(--color-muted);
}

.affiliation {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  align-items: center;
  gap: 0.45rem;
  font-size: 0.92rem;
  color: var(--color-secondary);
  text-align: center;
}

.affiliation-sep {
  color: #a1a1aa;
}

.site-nav {
  display: flex;
  justify-content: center;
  gap: 2rem;
  padding: 0.85rem 1.5rem;
  border-bottom: 1px solid var(--color-border);
  background: rgba(255, 255, 255, 0.92);
  backdrop-filter: blur(10px);
  position: sticky;
  top: 0;
  z-index: 10;
}

.nav-item {
  font-size: 0.82rem;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  font-weight: 700;
  color: var(--color-muted);
}

a.nav-item:hover,
a.nav-item:focus-visible {
  color: var(--color-accent);
  border-bottom-color: transparent;
}

.nav-item.current {
  color: var(--color-primary);
}

.nav-item.is-disabled {
  color: #a1a1aa;
  cursor: not-allowed;
}

.nav-item.lang-switch {
  color: var(--color-accent);
  border: 1px solid var(--color-accent);
  border-radius: 4px;
  padding: 0.1rem 0.5rem;
  font-size: 0.75rem;
}

.nav-item.lang-switch:hover {
  background: var(--color-accent);
  color: #fff;
  border-bottom-color: var(--color-accent);
}

main {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 3rem 1.5rem 4rem;
}

.page-intro {
  max-width: var(--content-width);
  margin: 0 auto 2.8rem;
  padding-bottom: 1.8rem;
  border-bottom: 1px solid var(--color-border);
}

.eyebrow {
  display: block;
  margin-bottom: 0.5rem;
  font-size: 0.74rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--color-accent);
}

.article-hero h2,
.chapter-section h2 {
  display: inline-block;
  margin-bottom: 1rem;
  padding-bottom: 0.4rem;
  border-bottom: 2px solid var(--color-primary);
  font-family: var(--font-serif);
  font-size: 1.5rem;
  font-weight: 600;
  color: var(--color-primary);
}

.page-intro h2 {
  display: block;
  margin-bottom: 0.9rem;
  padding-bottom: 0;
  border-bottom: none;
  font-family: var(--font-serif);
  font-size: clamp(2.15rem, 5vw, 3.15rem);
  font-weight: 600;
  line-height: 1.04;
  letter-spacing: -0.03em;
  color: var(--color-primary);
}

.page-intro p,
.article-hero p {
  max-width: 72ch;
  margin-bottom: 1rem;
  color: var(--color-secondary);
}

.summary-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.9rem;
  margin-top: 1.2rem;
}

.summary-card,
.tutorial-card,
.course-sidebar,
.article-sidebar,
.article-hero {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-card);
  box-shadow: var(--shadow-soft);
}

.summary-card,
.tutorial-card,
.article-hero {
  padding: 1rem 1.1rem;
}

.summary-label,
.tutorial-code,
.course-title,
.outline-title {
  display: inline-block;
  margin-bottom: 0.45rem;
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--color-accent);
}

.summary-card strong {
  display: block;
  margin-bottom: 0.35rem;
  font-family: var(--font-serif);
  font-size: 1rem;
  font-weight: 600;
  color: var(--color-primary);
}

.summary-card p,
.tutorial-meta,
.tutorial-excerpt {
  margin: 0;
  color: var(--color-muted);
}

.tutorial-excerpt {
  display: -webkit-box;
  -webkit-box-orient: vertical;
  -webkit-line-clamp: 4;
  overflow: hidden;
}

.chapter-section + .chapter-section {
  margin-top: 2.8rem;
}

.tutorial-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.9rem;
  margin-top: 1rem;
}

.tutorial-card h3 {
  margin-bottom: 0.35rem;
  font-family: var(--font-serif);
  font-size: 1.08rem;
  font-weight: 600;
  color: var(--color-primary);
}

.tutorial-link {
  display: inline-block;
  margin-top: 0.85rem;
  font-size: 0.9rem;
  font-weight: 700;
}

.article-layout {
  display: grid;
  grid-template-columns: 240px minmax(0, 1fr) 220px;
  gap: 1.5rem;
  align-items: start;
}

.article-main {
  min-width: 0;
}

.article-hero {
  margin-bottom: 1.8rem;
}

.article-code {
  margin-bottom: 0.45rem;
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--color-accent);
}

.article-hero .article-title {
  margin-bottom: 0.55rem;
  font-family: var(--font-serif);
  font-size: 2rem;
  line-height: 1.18;
  color: var(--color-primary);
}

.article-hero .article-subtitle {
  margin-bottom: 0;
}

.article-content {
  max-width: var(--content-width);
}

.article-content h2,
.article-content h3 {
  margin: 2rem 0 0.85rem;
  font-family: var(--font-serif);
  color: var(--color-primary);
}

.article-content h2 {
  font-size: 1.5rem;
}

.article-content h3 {
  font-size: 1.16rem;
}

.article-content p,
.article-content ul,
.article-content ol,
.article-content table,
.article-content pre,
.article-content .tutorial-figure,
.article-content .missing-image {
  margin-bottom: 1rem;
}

.article-content p,
.article-content li {
  color: var(--color-secondary);
}

.article-content ul,
.article-content ol {
  padding-left: 1.4rem;
}

.article-content li + li {
  margin-top: 0.45rem;
}

.article-content code {
  font-family: var(--font-mono);
  font-size: 0.92em;
  background: rgba(37, 99, 235, 0.08);
  color: var(--color-primary);
  padding: 0.1rem 0.3rem;
  border-radius: 6px;
}

.article-content pre {
  overflow-x: auto;
  background: #f5f7fb;
  border: 1px solid var(--color-border);
  border-radius: 12px;
  padding: 1rem 1.1rem;
}

.article-content pre code {
  display: block;
  padding: 0;
  background: transparent;
  border-radius: 0;
}

.article-content table {
  width: 100%;
  border-collapse: collapse;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
}

.article-content th,
.article-content td {
  padding: 0.7rem 0.8rem;
  border-bottom: 1px solid var(--color-border);
  text-align: left;
  vertical-align: top;
}

.article-content th {
  font-weight: 700;
  color: var(--color-primary);
  background: #f8fafc;
}

.tutorial-figure {
  padding: 0.9rem;
  border: 1px solid var(--color-border);
  border-radius: 12px;
  background: var(--color-surface);
  box-shadow: var(--shadow-soft);
}

.tutorial-figure img {
  display: block;
  width: 100%;
  height: auto;
  border-radius: 8px;
}

.tutorial-figure figcaption {
  margin-top: 0.65rem;
  font-size: 0.84rem;
  color: var(--color-muted);
  text-align: center;
}

.missing-image {
  padding: 0.8rem 1rem;
  border-left: 3px solid #b91c1c;
  background: #fff7f7;
  color: #991b1b;
  font-size: 0.9rem;
}

.course-sidebar,
.article-sidebar {
  position: sticky;
  top: 5.5rem;
  padding: 1rem 1.1rem;
}

.course-chapter + .course-chapter {
  margin-top: 1rem;
  padding-top: 1rem;
  border-top: 1px solid var(--color-border);
}

.course-chapter-name {
  margin-bottom: 0.55rem;
  font-family: var(--font-serif);
  font-size: 0.98rem;
  color: var(--color-primary);
}

.course-nav ul,
.outline-nav ul {
  list-style: none;
  padding-left: 0;
  margin: 0;
}

.course-nav li + li,
.outline-nav li + li {
  margin-top: 0.55rem;
}

.course-nav a,
.outline-nav a {
  border-bottom: none;
  color: var(--color-secondary);
  font-size: 0.9rem;
}

.course-nav a:hover,
.course-nav a:focus-visible,
.outline-nav a:hover,
.outline-nav a:focus-visible {
  color: var(--color-accent);
}

.course-link {
  display: block;
  padding: 0.35rem 0.45rem;
  border-radius: 8px;
  line-height: 1.45;
}

.course-link.current {
  color: var(--color-primary);
  background: rgba(37, 99, 235, 0.08);
}

.article-pagination {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin-top: 2.5rem;
  padding-top: 1.4rem;
  border-top: 1px solid var(--color-border);
}

.article-pagination a {
  display: inline-flex;
  flex-direction: column;
  gap: 0.15rem;
  border-bottom: none;
}

.pagination-label {
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--color-muted);
}

.pagination-title {
  font-family: var(--font-serif);
  color: var(--color-primary);
}

.site-footer {
  padding: 2rem 1.5rem;
  border-top: 1px solid var(--color-border);
  text-align: center;
  font-size: 0.8rem;
  color: var(--color-muted);
}

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

@media (max-width: 1080px) {
  .article-layout {
    grid-template-columns: 240px minmax(0, 1fr);
  }

  .article-sidebar {
    display: none;
  }
}

@media (max-width: 960px) {
  .article-layout {
    grid-template-columns: 1fr;
  }

  .course-sidebar,
  .article-sidebar {
    position: static;
  }
}

@media (max-width: 720px) {
  html {
    font-size: 16px;
  }

  .site-header h1 {
    font-size: 2.1rem;
  }

  .site-nav {
    gap: 1rem;
    flex-wrap: wrap;
  }

  .summary-grid,
  .tutorial-grid {
    grid-template-columns: 1fr;
  }

  .article-hero .article-title {
    font-size: 1.65rem;
  }

  .article-pagination {
    flex-direction: column;
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    transition: none !important;
    animation: none !important;
  }

  html {
    scroll-behavior: auto;
  }
}