:root {
  --navy-900: #0b1f3a;
  --navy-700: #12355b;
  --navy-500: #1a4d7a;
  --navy-300: #2a4d74;
  --gold-500: #c9a94a;
  --gold-400: #e8c66b;
  --ink-900: #1a1a1a;
  --ink-700: #2a2a2a;
  --ink-500: #4a5568;
  --ink-300: #6b7280;
  --paper: #ffffff;
  --bg-soft: #f5f7fa;
  --bg-sidebar: #f7f9fc;
  --border: #d9dfe6;
  --border-soft: #e5eaf0;
  --zebra: #f2f5f9;
  --highlight: #fcf9f0;
  --content-width: 820px;
  --sidebar-width: 280px;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }
body {
  margin: 0;
  font-family: "Source Serif Pro", "Charter", "Cambria", "Georgia", serif;
  font-size: 17px;
  line-height: 1.65;
  color: var(--ink-900);
  background: var(--paper);
}
a { color: var(--navy-700); text-decoration: none; border-bottom: 1px solid transparent; transition: border-color .2s; }
a:hover { border-bottom-color: var(--navy-500); }

/* ---------------- Hero ---------------- */
.hero {
  background: linear-gradient(160deg, #0b1f3a 0%, #12355b 55%, #1a4d7a 100%);
  color: #f5f5f0;
  padding: 70px 40px 60px;
  position: relative;
  overflow: hidden;
}
.hero::before {
  content: "";
  position: absolute;
  left: 40px; top: 50px;
  width: 80px; height: 3px;
  background: var(--gold-400);
}
.hero-inner { max-width: 1180px; margin: 0 auto; }
.hero .eyebrow {
  font-family: "Inter", "Segoe UI", "Arial", sans-serif;
  font-size: 12px;
  letter-spacing: 0.35em;
  text-transform: uppercase;
  color: var(--gold-400);
  margin-top: 30px;
}
.hero h1 {
  font-family: "Source Serif Pro", "Charter", "Cambria", serif;
  font-size: clamp(32px, 5vw, 56px);
  font-weight: 600;
  line-height: 1.1;
  margin: 18px 0 14px 0;
  color: #ffffff;
  max-width: 900px;
}
.hero .subtitle {
  font-family: "Inter", "Segoe UI", sans-serif;
  font-size: 18px;
  color: #cdd9e5;
  max-width: 800px;
  line-height: 1.45;
}
.hero .meta {
  margin-top: 36px;
  padding-top: 18px;
  border-top: 1px solid #3a5572;
  font-family: "Inter", "Segoe UI", sans-serif;
  font-size: 13px;
  color: #a9b8c9;
  letter-spacing: 0.04em;
  display: flex;
  flex-wrap: wrap;
  gap: 18px;
  justify-content: space-between;
}

/* ---------------- Layout ---------------- */
.layout {
  max-width: 1180px;
  margin: 0 auto;
  padding: 0 24px;
  display: grid;
  grid-template-columns: var(--sidebar-width) 1fr;
  gap: 48px;
  align-items: start;
}
@media (max-width: 900px) {
  .layout { grid-template-columns: 1fr; gap: 0; padding: 0 20px; }
  .sidebar { position: static; max-height: none; border-right: none; border-bottom: 1px solid var(--border); margin-top: 16px; padding: 12px 0; }
  .sidebar details { border: 1px solid var(--border); border-radius: 8px; padding: 10px 14px; background: var(--bg-sidebar); }
  .sidebar summary { cursor: pointer; font-family: "Inter", sans-serif; font-weight: 600; color: var(--navy-900); }
  .sidebar .nav-inner { margin-top: 10px; }
}
@media (min-width: 901px) {
  .sidebar details summary { display: none; }
  .sidebar details .nav-inner { display: block !important; }
}

/* ---------------- Sidebar ---------------- */
.sidebar {
  position: sticky;
  top: 20px;
  max-height: calc(100vh - 40px);
  overflow-y: auto;
  padding: 32px 0 24px 0;
  font-family: "Inter", "Segoe UI", sans-serif;
  font-size: 14px;
  line-height: 1.45;
}
.sidebar .nav-title {
  font-size: 11px;
  letter-spacing: 0.22em;
  text-transform: uppercase;
  color: var(--ink-500);
  margin-bottom: 14px;
  font-weight: 700;
}
.sidebar ol {
  list-style: none;
  padding: 0;
  margin: 0;
  counter-reset: navitem;
}
.sidebar li {
  margin: 0;
  counter-increment: navitem;
}
.sidebar li a {
  display: block;
  padding: 7px 12px;
  color: var(--ink-700);
  border-left: 3px solid transparent;
  border-bottom: none;
  border-radius: 0 4px 4px 0;
  transition: background .15s, border-color .15s, color .15s;
}
.sidebar li a:hover {
  background: var(--bg-sidebar);
  color: var(--navy-900);
  border-left-color: var(--gold-500);
}
.sidebar li a.active {
  background: var(--bg-sidebar);
  color: var(--navy-900);
  border-left-color: var(--navy-700);
  font-weight: 600;
}

/* ---------------- Content ---------------- */
.content {
  max-width: var(--content-width);
  padding: 36px 0 80px 0;
}
.content h1, .content h2, .content h3, .content h4 {
  font-family: "Inter", "Segoe UI", "Arial", sans-serif;
  color: var(--navy-900);
  line-height: 1.25;
  font-weight: 700;
  scroll-margin-top: 20px;
}
.content > h1:first-child { margin-top: 0; }
.content h1 {
  font-size: 30px;
  margin: 36px 0 10px 0;
  padding-bottom: 10px;
  border-bottom: 2px solid var(--gold-500);
}
.content h2 {
  font-size: 24px;
  margin: 42px 0 12px 0;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--border-soft);
}
.content h3 {
  font-size: 19px;
  color: var(--navy-700);
  margin: 28px 0 8px 0;
}
.content h4 {
  font-size: 16px;
  color: var(--navy-300);
  margin: 22px 0 6px 0;
  font-weight: 700;
}
.content p {
  margin: 0 0 14px 0;
  color: var(--ink-700);
}
.content strong { color: var(--navy-900); }
.content ul, .content ol {
  margin: 0 0 16px 0;
  padding-left: 24px;
}
.content li { margin-bottom: 6px; color: var(--ink-700); }
.content hr {
  border: none;
  border-top: 1px solid var(--border);
  margin: 32px 0;
}

/* ---------------- Tables ---------------- */
.content .table-wrap {
  margin: 14px 0 22px 0;
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
  border-radius: 8px;
  border: 1px solid var(--border);
}
.content table {
  width: 100%;
  border-collapse: collapse;
  font-size: 14px;
  font-family: "Inter", "Segoe UI", "Arial", sans-serif;
  background: var(--paper);
}
.content th {
  background: var(--navy-900);
  color: #ffffff;
  padding: 10px 14px;
  text-align: left;
  font-weight: 600;
  border: 1px solid var(--navy-900);
}
.content td {
  padding: 8px 14px;
  border: 1px solid var(--border-soft);
  vertical-align: top;
  color: var(--ink-700);
}
.content tbody tr:nth-child(even) td { background: var(--zebra); }
.content th[align="right"], .content td[align="right"] { text-align: right; }
.content th[align="center"], .content td[align="center"] { text-align: center; }

/* ---------------- Figures ---------------- */
.content figure {
  margin: 28px 0 28px 0;
  padding: 14px;
  background: var(--paper);
  border: 1px solid var(--border-soft);
  border-radius: 10px;
  box-shadow: 0 1px 2px rgba(11, 31, 58, 0.04), 0 4px 12px rgba(11, 31, 58, 0.04);
}
.content figure img {
  display: block;
  max-width: 100%;
  height: auto;
  margin: 0 auto;
  border-radius: 4px;
}
.content figure figcaption {
  margin-top: 12px;
  font-size: 13px;
  color: var(--ink-500);
  font-family: "Inter", "Segoe UI", sans-serif;
  line-height: 1.5;
  text-align: left;
}

/* ---------------- Code ---------------- */
.content code {
  font-family: "JetBrains Mono", "Consolas", "Menlo", monospace;
  font-size: 13.5px;
  background: var(--zebra);
  padding: 1px 5px;
  border-radius: 4px;
  color: var(--navy-700);
}
.content pre {
  background: var(--zebra);
  border: 1px solid var(--border-soft);
  border-radius: 8px;
  padding: 14px 16px;
  overflow-x: auto;
  font-size: 13px;
  line-height: 1.5;
}
.content pre code {
  background: transparent;
  padding: 0;
  color: var(--ink-900);
}

/* ---------------- Math ---------------- */
.math-display {
  margin: 16px 0 20px 0;
  text-align: center;
  overflow-x: auto;
  padding: 8px 0;
  font-size: 17px;
}
.math-inline { white-space: nowrap; }
.katex-display > .katex { max-width: 100%; overflow-x: auto; overflow-y: hidden; }

/* ---------------- Footer ---------------- */
.site-footer {
  border-top: 1px solid var(--border);
  padding: 22px 24px;
  font-family: "Inter", "Segoe UI", sans-serif;
  font-size: 13px;
  color: var(--ink-500);
  text-align: center;
}