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

:root {
  --bg: #fff;
  --bg-2: #f8f8f8;
  --text: #111;
  --text-2: #444;
  --text-3: #888;
  --border: #e5e5e5;
  --accent: #2563eb;
  --font: system-ui, -apple-system, sans-serif;
  --mono: 'Menlo', 'Monaco', monospace;
}

html { scroll-behavior: smooth; }
body { font-family: var(--font); background: var(--bg); color: var(--text); }

/* Nav */
.site-nav {
  position: sticky;
  top: 0;
  z-index: 100;
  display: flex;
  align-items: center;
  gap: 24px;
  padding: 16px 40px;
  background: rgba(255,255,255,0.9);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
}
.nav-back { font-size: 0.8125rem; color: var(--text-3); text-decoration: none; }
.nav-back:hover { color: var(--text); }
.nav-brand { font-weight: 700; font-size: 0.9rem; flex: 1; }
.nav-links { display: flex; gap: 20px; }
.nav-links a { font-size: 0.875rem; color: var(--text-2); text-decoration: none; }
.nav-links a:hover { color: var(--text); }

/* Hero */
.hero {
  min-height: 80vh;
  display: flex;
  align-items: center;
  border-bottom: 1px solid var(--border);
}
.hero-inner {
  max-width: 860px;
  margin: 0 auto;
  padding: 80px 40px;
  width: 100%;
}
.hero-label {
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--text-3);
  margin-bottom: 28px;
}
.hero-title {
  font-size: 4rem;
  line-height: 1.05;
  letter-spacing: -0.05em;
  margin-bottom: 24px;
}
.hero-title span { display: block; }
.title-accent { color: var(--accent); }
.hero-sub {
  font-size: 1.0625rem;
  color: var(--text-2);
  max-width: 560px;
  line-height: 1.7;
  margin-bottom: 36px;
}
.hero-actions { display: flex; gap: 12px; flex-wrap: wrap; }
.btn-primary {
  display: inline-block;
  padding: 11px 24px;
  background: var(--accent);
  color: #fff;
  text-decoration: none;
  font-size: 0.9rem;
  font-weight: 500;
  border-radius: 6px;
  transition: background 0.15s;
}
.btn-primary:hover { background: #1d4ed8; }
.btn-ghost {
  display: inline-block;
  padding: 11px 24px;
  color: var(--text-2);
  text-decoration: none;
  font-size: 0.9rem;
  border: 1px solid var(--border);
  border-radius: 6px;
  transition: border-color 0.15s, color 0.15s;
}
.btn-ghost:hover { border-color: #bbb; color: var(--text); }

/* Concepts section */
.concepts {
  padding: 80px 0;
  border-bottom: 1px solid var(--border);
}
.concepts-inner { max-width: 860px; margin: 0 auto; padding: 0 40px; }
h2 { font-size: 1.25rem; letter-spacing: -0.02em; margin-bottom: 32px; }
.concept-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 16px;
}
.concept-card {
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 24px;
  transition: border-color 0.12s;
}
.concept-card:hover { border-color: #bbb; }
.concept-icon { font-size: 1.25rem; margin-bottom: 12px; color: var(--text-3); }
.concept-card h3 { font-size: 1rem; font-family: var(--mono); margin-bottom: 8px; }
.concept-card p { font-size: 0.8375rem; color: var(--text-2); line-height: 1.6; margin-bottom: 12px; }
.concept-card code {
  font-family: var(--mono);
  font-size: 0.73rem;
  color: var(--text-3);
  line-height: 1.7;
  display: block;
}

/* Timeline demo */
.timeline-demo {
  padding: 80px 0;
}
.timeline-inner { max-width: 860px; margin: 0 auto; padding: 0 40px; }
.code-block {
  background: var(--bg-2);
  border: 1px solid var(--border);
  border-radius: 8px;
  overflow: auto;
  margin-bottom: 16px;
}
.code-block pre { padding: 24px; }
.code-block code { font-family: var(--mono); font-size: 0.8rem; color: var(--text); line-height: 1.75; }
.code-note { font-size: 0.8375rem; color: var(--text-3); line-height: 1.6; }
.code-note code { background: var(--bg-2); border: 1px solid var(--border); padding: 1px 5px; border-radius: 3px; font-size: 0.8em; font-family: var(--mono); color: var(--text); }

@media (max-width: 640px) {
  .site-nav { padding: 14px 20px; }
  .hero-inner { padding: 60px 20px; }
  .hero-title { font-size: 2.5rem; }
  .concept-grid { grid-template-columns: 1fr; }
  .concepts-inner,
  .timeline-inner { padding: 0 20px; }
}