:root {
  --bg: #f8fafc;
  --surface: #ffffff;
  --surface-soft: #eef3f8;
  --text: #0f172a;
  --muted: #64748b;
  --accent: #1e40af;
  --accent-2: #8a4d2f;
  --gold: #b45309;
  --border: #e2e8f0;
  --shadow: 0 1px 3px rgba(0,0,0,0.08);
  --maxw: 1080px;
  --serif: 'Crimson Pro', Georgia, serif;
  --sans: 'Source Sans 3', Helvetica, Arial, sans-serif;
}

* { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: var(--sans);
  color: var(--text);
  background: var(--bg);
  line-height: 1.75;
}

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }
img { max-width: 100%; display: block; }

.container {
  width: min(var(--maxw), calc(100% - 32px));
  margin: 0 auto;
}

.site-header {
  background: var(--surface);
  border-bottom: 1px solid var(--border);
}

.topbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 18px;
  padding: 14px 0;
  flex-wrap: wrap;
}

.brand {
  font-family: var(--serif);
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--text);
}

.brand span { color: var(--gold); }

nav {
  display: flex;
  gap: 18px;
  flex-wrap: wrap;
}

nav a {
  color: var(--muted);
  font-weight: 600;
  font-size: 0.95rem;
}

.hero {
  background: #1e293b;
  color: #fff;
  padding: 54px 0 42px;
}

.eyebrow {
  display: inline-block;
  font-size: 0.78rem;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: #e2e8f0;
  margin-bottom: 10px;
}

.hero h1 {
  font-family: var(--serif);
  font-size: clamp(2rem, 4vw, 3rem);
  line-height: 1.12;
  max-width: 920px;
  margin-bottom: 14px;
}

.hero p {
  color: #cbd5e1;
  max-width: 780px;
  font-size: 1.05rem;
}

.byline {
  display: flex;
  flex-wrap: wrap;
  gap: 8px 18px;
  font-size: 0.95rem;
  color: #dbe4ee;
  margin-top: 14px;
}

.article-layout {
  display: grid;
  grid-template-columns: 1.4fr 0.6fr;
  gap: 22px;
  padding: 44px 0 60px;
  align-items: start;
}

.article-body,
.sidebar-card,
.index-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 8px;
  box-shadow: var(--shadow);
}

.article-body { padding: 32px 34px; }
.sidebar-card { padding: 22px; }
.sidebar-card + .sidebar-card { margin-top: 22px; }

.lead {
  color: #475569;
  font-size: 1.08rem;
  margin-bottom: 18px;
}

h2 {
  font-family: var(--serif);
  font-size: 1.58rem;
  color: #2f3945;
  margin: 28px 0 12px;
  line-height: 1.2;
}

h2:first-child { margin-top: 0; }

h3 {
  font-family: var(--serif);
  font-size: 1.18rem;
  color: #2f3945;
  margin: 20px 0 8px;
}

p { color: var(--muted); margin-bottom: 14px; }
ul, ol { color: var(--muted); padding-left: 22px; margin-bottom: 14px; }
li + li { margin-top: 7px; }

.article-figure {
  max-width: 520px;
  margin: 22px auto 26px;
  border: 1px solid var(--border);
  border-radius: 8px;
  overflow: hidden;
  background: #fff;
}

.article-figure img {
  width: 100%;
  height: auto;
  object-fit: contain;
  background: #fff;
}

.article-figure figcaption {
  border-top: 1px solid var(--border);
  color: var(--muted);
  font-size: 0.92rem;
  padding: 10px 12px;
  background: #f8fafc;
}

.note,
.equation-box {
  border-radius: 8px;
  margin: 18px 0;
}

.note {
  background: #eef2f7;
  border: 1px solid #d7dee7;
  padding: 14px 16px;
  color: #475569;
}

.equation-box {
  background: var(--surface-soft);
  border: 1px solid #c9d1da;
  border-left: 4px solid #5b6774;
  padding: 16px 18px 12px;
  overflow-x: auto;
}

.meta-list {
  list-style: none;
  padding-left: 0;
  margin-bottom: 0;
}

.meta-list li {
  padding: 10px 0;
  border-top: 1px solid var(--border);
  color: var(--muted);
}

.meta-list li:first-child {
  border-top: 0;
  padding-top: 0;
}

.index-main { padding: 44px 0 60px; }

.index-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 18px;
  margin-top: 24px;
}

.index-card {
  padding: 22px;
  display: flex;
  flex-direction: column;
  min-height: 260px;
}

.index-card h2 {
  font-size: 1.28rem;
  margin: 8px 0 10px;
}

.index-card p { margin-bottom: 12px; }

.tag {
  display: inline-block;
  width: fit-content;
  padding: 4px 10px;
  border-radius: 999px;
  background: var(--surface-soft);
  color: #475569;
  font-size: 0.82rem;
  font-weight: 700;
}

.card-link {
  margin-top: auto;
  font-weight: 700;
}

footer {
  background: #12253f;
  color: rgba(255,255,255,0.72);
  padding: 26px 0;
  font-size: 0.9rem;
}

footer a { color: rgba(255,255,255,0.86); }

@media (max-width: 960px) {
  .article-layout { grid-template-columns: 1fr; }
  .index-grid { grid-template-columns: repeat(2, 1fr); }
}

@media (max-width: 680px) {
  .article-body { padding: 24px 20px; }
  .index-grid { grid-template-columns: 1fr; }
  .index-card { min-height: 0; }
}