/* Modern personal research blog — inspired by ekzhang.com and BAIR blog */
/* Clean, minimal, high-credibility academic aesthetic */

:root {
  --text: #1a1a2e;
  --muted: #6b7280;
  --link: #2563eb;
  --link-hover: #1d4ed8;
  --border: #e5e7eb;
  --bg: #ffffff;
  --callout-bg: #f8fafc;
  --code-bg: #f3f4f6;
  --max-width: 680px;
  --font-sans: -apple-system, BlinkMacSystemFont, 'Inter', 'Segoe UI', system-ui, sans-serif;
  --font-serif: 'Georgia', 'Cambria', 'Times New Roman', serif;
  --font-mono: 'SF Mono', 'Fira Code', 'Consolas', monospace;
}

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

body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-sans);
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

/* ========== Homepage styles ========== */
.site-header {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 80px 24px 0;
}

.site-header h1 {
  font-size: 1.6rem;
  font-weight: 600;
  letter-spacing: -0.02em;
  margin: 0 0 8px;
}

.site-header .tagline {
  color: var(--muted);
  font-size: 1rem;
  line-height: 1.6;
  margin: 0 0 48px;
}

.site-nav {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 24px;
  display: flex;
  gap: 24px;
  border-bottom: 1px solid var(--border);
  padding-bottom: 16px;
  margin-bottom: 48px;
}

.site-nav a {
  color: var(--muted);
  text-decoration: none;
  font-size: 0.9rem;
  font-weight: 500;
  transition: color 0.15s;
}

.site-nav a:hover,
.site-nav a.active {
  color: var(--text);
}

/* ========== Essay list on homepage ========== */
.essay-list {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 24px 80px;
}

.essay-list h2 {
  font-size: 0.85rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--muted);
  margin: 0 0 24px;
}

.essay-card {
  margin-bottom: 36px;
  padding-bottom: 36px;
  border-bottom: 1px solid var(--border);
}

.essay-card:last-child {
  border-bottom: none;
}

.essay-card h3 {
  margin: 0 0 8px;
  font-size: 1.2rem;
  font-weight: 600;
  line-height: 1.35;
  letter-spacing: -0.01em;
}

.essay-card h3 a {
  color: var(--text);
  text-decoration: none;
  transition: color 0.15s;
}

.essay-card h3 a:hover {
  color: var(--link);
}

.essay-card .essay-date {
  font-size: 0.85rem;
  color: var(--muted);
  margin: 0 0 10px;
}

.essay-card p {
  margin: 0;
  font-size: 0.95rem;
  line-height: 1.65;
  color: #374151;
}

/* ========== Essay page styles ========== */
.essay-shell {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 60px 24px 100px;
}

.essay-backlink {
  margin-bottom: 40px;
}

.essay-backlink a {
  color: var(--muted);
  text-decoration: none;
  font-size: 0.9rem;
  font-weight: 500;
  transition: color 0.15s;
}

.essay-backlink a:hover {
  color: var(--text);
}

.essay-title {
  margin: 0 0 12px;
  font-size: clamp(1.8rem, 4vw, 2.4rem);
  font-weight: 700;
  line-height: 1.15;
  letter-spacing: -0.025em;
  color: var(--text);
}

.essay-subtitle {
  margin: 0 0 16px;
  color: var(--muted);
  font-size: 1.1rem;
  line-height: 1.5;
  font-weight: 400;
}

.essay-meta {
  margin: 0 0 36px;
  color: var(--muted);
  font-size: 0.85rem;
  font-weight: 500;
}

.essay-callout {
  margin: 0 0 48px;
  padding: 16px 20px;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--callout-bg);
  font-size: 0.95rem;
  line-height: 1.6;
}

.essay-callout a {
  color: var(--link);
  text-decoration: none;
}

.essay-callout a:hover {
  text-decoration: underline;
}

/* ========== Essay content ========== */
.essay-content {
  font-family: var(--font-serif);
  font-size: 1.08rem;
  line-height: 1.82;
  color: #1f2937;
}

.essay-content p {
  margin: 0 0 1.4em;
}

.essay-content h2 {
  font-family: var(--font-sans);
  font-size: 1.35rem;
  font-weight: 650;
  line-height: 1.3;
  letter-spacing: -0.015em;
  margin: 2.8em 0 0.8em;
  color: var(--text);
}

.essay-content h3 {
  font-family: var(--font-sans);
  font-size: 1.08rem;
  font-weight: 600;
  line-height: 1.4;
  margin: 2em 0 0.6em;
  color: var(--text);
}

.essay-content ul,
.essay-content ol {
  margin: 0 0 1.4em;
  padding-left: 1.3em;
}

.essay-content li {
  margin-bottom: 0.4em;
  line-height: 1.7;
}

.essay-content li + li {
  margin-top: 0.3em;
}

.essay-content blockquote {
  margin: 1.8em 0;
  padding: 0 0 0 1.2em;
  border-left: 3px solid var(--link);
  color: #374151;
  font-style: italic;
}

.essay-content blockquote p {
  margin-bottom: 0.6em;
}

.essay-content strong {
  font-weight: 700;
  color: var(--text);
}

.essay-content a {
  color: var(--link);
  text-decoration: underline;
  text-decoration-color: rgba(37, 99, 235, 0.3);
  text-underline-offset: 3px;
  transition: text-decoration-color 0.15s;
}

.essay-content a:hover {
  text-decoration-color: var(--link);
}

.essay-content code {
  font-family: var(--font-mono);
  font-size: 0.88em;
  background: var(--code-bg);
  padding: 2px 6px;
  border-radius: 4px;
}

.essay-content pre {
  background: #1e293b;
  color: #e2e8f0;
  padding: 16px 20px;
  border-radius: 8px;
  overflow-x: auto;
  font-family: var(--font-mono);
  font-size: 0.88rem;
  line-height: 1.6;
  margin: 1.6em 0;
}

.essay-content hr {
  border: none;
  border-top: 1px solid var(--border);
  margin: 2.4em 0;
}

/* ========== Dividers and footer ========== */
.essay-divider {
  border: none;
  border-top: 1px solid var(--border);
  margin: 2.8em 0;
}

.essay-footer-note {
  margin-top: 48px;
  padding-top: 24px;
  border-top: 1px solid var(--border);
}

.essay-footer-note a {
  color: var(--muted);
  text-decoration: none;
  font-size: 0.9rem;
  font-weight: 500;
}

.essay-footer-note a:hover {
  color: var(--text);
}

/* ========== Site footer ========== */
.site-footer {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 32px 24px 64px;
  border-top: 1px solid var(--border);
  color: var(--muted);
  font-size: 0.85rem;
}

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

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

/* ========== Responsive ========== */
@media (max-width: 700px) {
  .site-header {
    padding-top: 48px;
  }

  .essay-shell {
    padding: 40px 18px 80px;
  }

  .essay-content {
    font-size: 1.02rem;
    line-height: 1.75;
  }

  .essay-title {
    font-size: 1.6rem;
  }
}

/* ========== AI agent friendly: structured data hint ========== */
/* Semantic HTML + schema.org compatible structure */