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

:root {
    --bg: #0a0a0b;
    --bg-card: #111113;
    --bg-card-hover: #18181b;
    --border: #27272a;
    --border-hover: #3f3f46;
    --text: #fafafa;
    --text-muted: #a1a1aa;
    --text-dim: #71717a;
    --accent: #3b82f6;
    --accent-glow: rgba(59, 130, 246, 0.15);
    --green: #22c55e;
    --orange: #f97316;
    --purple: #a855f7;
    --red: #ef4444;
    --yellow: #eab308;
    --cyan: #06b6d4;
    --radius: 12px;
    --radius-sm: 8px;
    --font: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
    --mono: 'JetBrains Mono', 'Fira Code', monospace;
}

html { scroll-behavior: smooth; }

body {
    font-family: var(--font);
    background: var(--bg);
    color: var(--text);
    line-height: 1.6;
    min-height: 100vh;
}

/* ── Top Nav ───────────────────────────────────── */
.top-nav {
    position: sticky;
    top: 0;
    z-index: 100;
    background: rgba(10, 10, 11, 0.8);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    border-bottom: 1px solid var(--border);
}

.nav-inner {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 24px;
    height: 60px;
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.logo {
    font-weight: 700;
    font-size: 1.05rem;
    color: var(--text);
    text-decoration: none;
    letter-spacing: -0.02em;
}

.logo-icon {
    display: inline-block;
    margin-right: 8px;
    filter: grayscale(0.3);
}

.menu-toggle {
    display: none;
    background: none;
    border: none;
    color: var(--text);
    font-size: 1.5rem;
    cursor: pointer;
}

/* ── Hero ──────────────────────────────────────── */
.hero {
    padding: 80px 24px 60px;
    text-align: center;
    background:
        radial-gradient(ellipse 60% 50% at 50% 0%, rgba(59, 130, 246, 0.08) 0%, transparent 100%),
        var(--bg);
    border-bottom: 1px solid var(--border);
}

.hero-content { max-width: 700px; margin: 0 auto; }

.hero h1 {
    font-size: clamp(2rem, 5vw, 3.2rem);
    font-weight: 800;
    letter-spacing: -0.03em;
    line-height: 1.15;
    margin-bottom: 20px;
    background: linear-gradient(135deg, #fff 0%, #a1a1aa 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.hero-sub {
    font-size: 1.1rem;
    color: var(--text-muted);
    margin-bottom: 36px;
    max-width: 560px;
    margin-left: auto;
    margin-right: auto;
}

.hero-stats {
    display: flex;
    gap: 12px;
    justify-content: center;
    flex-wrap: wrap;
}

.stat {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 99px;
    padding: 8px 18px;
    font-size: 0.82rem;
    font-weight: 500;
    color: var(--text-muted);
}

.stat-num {
    color: var(--text);
    font-weight: 700;
    font-family: var(--mono);
}

/* ── Container ─────────────────────────────────── */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 24px;
}

.section-header {
    max-width: 1200px;
    margin: 0 auto;
    padding: 64px 24px 0;
}

.section-header h2 {
    font-size: 1.5rem;
    font-weight: 700;
    margin-bottom: 8px;
    letter-spacing: -0.02em;
}

.section-header p {
    color: var(--text-muted);
    font-size: 0.95rem;
}

/* ── Card Grid ─────────────────────────────────── */
.card-grid {
    max-width: 1200px;
    margin: 0 auto;
    padding: 40px 24px 80px;
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(340px, 1fr));
    gap: 20px;
}

.card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    display: flex;
    align-items: flex-start;
    gap: 18px;
    padding: 28px;
    text-decoration: none;
    color: inherit;
    transition: all 0.25s ease;
    position: relative;
    overflow: hidden;
}

.card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 2px;
    background: linear-gradient(90deg, var(--accent), transparent);
    opacity: 0;
    transition: opacity 0.25s ease;
}

.card:hover {
    background: var(--bg-card-hover);
    border-color: var(--border-hover);
    transform: translateY(-2px);
}

.card:hover::before { opacity: 1; }

.card-icon {
    font-size: 2rem;
    flex-shrink: 0;
    width: 52px;
    height: 52px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: rgba(255,255,255,0.03);
    border-radius: var(--radius-sm);
    border: 1px solid var(--border);
}

.card-body { flex: 1; min-width: 0; }

.card-tag {
    font-size: 0.7rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    color: var(--accent);
    margin-bottom: 6px;
    display: block;
}

.card h3 {
    font-size: 1.1rem;
    font-weight: 700;
    margin-bottom: 8px;
    letter-spacing: -0.01em;
}

.card p {
    font-size: 0.88rem;
    color: var(--text-muted);
    line-height: 1.55;
    margin-bottom: 14px;
}

.card p code {
    background: rgba(255,255,255,0.06);
    padding: 2px 6px;
    border-radius: 4px;
    font-family: var(--mono);
    font-size: 0.82rem;
}

.card-link {
    font-size: 0.82rem;
    font-weight: 600;
    color: var(--accent);
}

/* ── Footer ────────────────────────────────────── */
footer {
    text-align: center;
    padding: 32px 24px;
    border-top: 1px solid var(--border);
    color: var(--text-dim);
    font-size: 0.82rem;
}

/* ── Mobile ────────────────────────────────────── */
@media (max-width: 640px) {
    .hero { padding: 56px 20px 40px; }
    .card-grid { grid-template-columns: 1fr; padding: 32px 20px 60px; }
    .card { padding: 22px; }
    .menu-toggle { display: block; }
}

/* ── Topic page styles ─────────────────────────── */
.topic-hero {
    padding: 60px 24px 40px;
    border-bottom: 1px solid var(--border);
    background:
        radial-gradient(ellipse 60% 50% at 50% 0%, rgba(59, 130, 246, 0.06) 0%, transparent 100%),
        var(--bg);
}

.topic-hero .container {
    padding: 0 24px;
}

.breadcrumb {
    font-size: 0.82rem;
    color: var(--text-dim);
    margin-bottom: 16px;
}

.breadcrumb a {
    color: var(--text-muted);
    text-decoration: none;
}

.breadcrumb a:hover { color: var(--accent); }

.topic-hero h1 {
    font-size: clamp(1.8rem, 4vw, 2.6rem);
    font-weight: 800;
    letter-spacing: -0.03em;
    margin-bottom: 12px;
    background: linear-gradient(135deg, #fff 0%, #a1a1aa 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.topic-hero p {
    color: var(--text-muted);
    font-size: 1rem;
    max-width: 600px;
}

.topic-content {
    max-width: 800px;
    margin: 0 auto;
    padding: 48px 24px 80px;
}

.topic-content h2 {
    font-size: 1.35rem;
    font-weight: 700;
    margin-top: 48px;
    margin-bottom: 16px;
    letter-spacing: -0.02em;
    padding-bottom: 8px;
    border-bottom: 1px solid var(--border);
}

.topic-content h2:first-child { margin-top: 0; }

.topic-content h3 {
    font-size: 1.05rem;
    font-weight: 600;
    margin-top: 32px;
    margin-bottom: 10px;
    color: var(--text);
}

.topic-content p {
    margin-bottom: 14px;
    color: var(--text-muted);
    line-height: 1.7;
}

.topic-content code {
    background: rgba(255,255,255,0.06);
    padding: 2px 7px;
    border-radius: 4px;
    font-family: var(--mono);
    font-size: 0.85em;
    color: #e4e4e7;
}

.topic-content pre {
    background: #0f0f11;
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    padding: 20px;
    margin: 16px 0 24px;
    overflow-x: auto;
    font-family: var(--mono);
    font-size: 0.85rem;
    line-height: 1.65;
    color: #e4e4e7;
}

.topic-content pre code {
    background: none;
    padding: 0;
    font-size: inherit;
}

.topic-content ul, .topic-content ol {
    margin: 12px 0 20px 24px;
    color: var(--text-muted);
}

.topic-content li { margin-bottom: 8px; line-height: 1.6; }

.topic-content blockquote {
    border-left: 3px solid var(--accent);
    padding: 12px 20px;
    margin: 20px 0;
    background: var(--accent-glow);
    border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
    color: var(--text-muted);
}

.topic-content table {
    width: 100%;
    border-collapse: collapse;
    margin: 20px 0;
    font-size: 0.9rem;
}

.topic-content th, .topic-content td {
    text-align: left;
    padding: 10px 14px;
    border: 1px solid var(--border);
}

.topic-content th {
    background: var(--bg-card);
    font-weight: 600;
    color: var(--text);
}

.topic-content td { color: var(--text-muted); }

.callout {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    padding: 20px 24px;
    margin: 24px 0;
}

.callout-title {
    font-weight: 600;
    font-size: 0.85rem;
    margin-bottom: 8px;
    display: flex;
    align-items: center;
    gap: 8px;
}

.callout p { margin-bottom: 0; font-size: 0.9rem; }

/* ── TOC sidebar ───────────────────────────────── */
.topic-layout {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 24px;
    display: grid;
    grid-template-columns: 1fr 220px;
    gap: 48px;
}

.topic-layout .topic-content { max-width: none; padding-top: 48px; padding-bottom: 80px; }

.toc {
    position: sticky;
    top: 80px;
    align-self: start;
    padding: 20px 0;
}

.toc h4 {
    font-size: 0.7rem;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    color: var(--text-dim);
    margin-bottom: 12px;
}

.toc ul { list-style: none; margin: 0; padding: 0; }

.toc li {
    margin-bottom: 6px;
}

.toc a {
    font-size: 0.82rem;
    color: var(--text-dim);
    text-decoration: none;
    transition: color 0.15s;
    display: block;
    padding: 3px 0 3px 12px;
    border-left: 2px solid var(--border);
}

.toc a:hover { color: var(--text); border-left-color: var(--accent); }

@media (max-width: 900px) {
    .topic-layout { grid-template-columns: 1fr; }
    .toc { display: none; }
}