:root {
  --accent: #0b4f6c;
  --accent-dark: #07384d;
  --text: #17212b;
  --muted: #5b6673;
  --line: #d8e1e8;
  --paper: #ffffff;
  --soft: #f6f9fb;
  --content-width: 920px;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  background: var(--soft);
  color: var(--text);
  font-family: Georgia, "Times New Roman", serif;
  font-size: 18px;
  line-height: 1.7;
}

a { color: var(--accent); text-decoration: none; }
a:hover, a:focus { color: var(--accent-dark); text-decoration: underline; }

.page {
  max-width: calc(var(--content-width) + 48px);
  margin: 0 auto;
  padding: 36px 24px 64px;
}

.top-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 10px 12px;
  margin-bottom: 36px;
  padding-bottom: 16px;
  border-bottom: 1px solid var(--line);
  font-family: Arial, Helvetica, sans-serif;
  font-size: 14px;
}

.top-nav a {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 38px;
  padding: 8px 13px;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: var(--paper);
  color: var(--accent);
  text-decoration: none;
}

.top-nav a:hover,
.top-nav a:focus {
  background: #eef6f9;
  color: var(--accent-dark);
  text-decoration: none;
}

.hero, .content-section, .local-toc, .page-nav, .program-footer, .related, .download-box {
  max-width: var(--content-width);
  margin-left: auto;
  margin-right: auto;
}

.hero { margin-bottom: 36px; }

.eyebrow {
  margin: 0 0 8px;
  color: var(--muted);
  font-family: Arial, Helvetica, sans-serif;
  font-size: 14px;
  letter-spacing: 0.02em;
  text-transform: uppercase;
}

h1, h2, h3 { color: var(--accent-dark); line-height: 1.2; }
h1 { margin: 0; font-size: 42px; font-weight: 600; }
.subtitle { margin: 8px 0 24px; color: var(--muted); font-family: Arial, Helvetica, sans-serif; font-size: 18px; }
.question { margin: 22px 0 10px; color: var(--text); font-size: 25px; line-height: 1.35; }

.content-section {
  padding: 28px 0;
  border-top: 1px solid var(--line);
}

.content-section h2 { margin: 0 0 18px; font-size: 27px; }
.content-section h3 { margin: 28px 0 10px; font-size: 21px; }
.content-section p { margin: 0 0 16px; }
.content-section ul, .content-section ol { margin: 0 0 18px; padding-left: 24px; }
.content-section li { margin: 6px 0; }
.content-section .item {
  margin: 16px 0 10px;
}

.lecture-body h2, .lecture-body h3 { scroll-margin-top: 24px; }
.aim, .note, .related, .download-box, .editorial-note {
  margin: 24px auto;
  padding: 18px 20px;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: var(--paper);
}

.aim, .note, .related, .download-box, .editorial-note {
  font-family: Arial, Helvetica, sans-serif;
  font-size: 15px;
  line-height: 1.55;
}

.note p, .related p, .download-box p, .editorial-note p { margin-bottom: 10px; }
.editorial-note h2 { margin: 0 0 8px; font-size: 18px; }
.editorial-note p { margin: 0; color: var(--muted); }

.local-toc {
  margin-bottom: 30px;
  padding: 18px 20px;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: var(--paper);
  font-family: Arial, Helvetica, sans-serif;
  font-size: 14px;
}

.local-toc h2 { margin: 0 0 10px; font-size: 18px; }
.local-toc ul { margin: 0; padding-left: 20px; }
.local-toc li { margin: 5px 0; }
.local-toc .toc-sub { margin-left: 16px; }

.program-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 16px;
  margin-top: 22px;
}

.program-card {
  display: block;
  min-height: 160px;
  padding: 18px;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: var(--paper);
  color: inherit;
  text-decoration: none;
}

.program-card:hover, .program-card:focus { background: #eef6f9; text-decoration: none; }
.program-card h3 { margin: 0 0 8px; font-family: Arial, Helvetica, sans-serif; font-size: 18px; }
.program-card p { margin: 0; color: var(--muted); font-family: Arial, Helvetica, sans-serif; font-size: 14px; line-height: 1.55; }

.button-row { display: flex; flex-wrap: wrap; gap: 10px; margin: 22px 0 0; }
.button-link {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 38px;
  padding: 8px 13px;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: var(--paper);
  color: var(--accent);
  font-family: Arial, Helvetica, sans-serif;
  font-size: 14px;
  text-decoration: none;
}
.button-link:hover, .button-link:focus { background: #eef6f9; text-decoration: none; }

.equation {
  overflow-x: auto;
  margin: 20px 0;
  padding: 14px 42px 14px 0;
  position: relative;
}

.equation-number {
  position: absolute;
  right: 0;
  top: 50%;
  transform: translateY(-50%);
  color: var(--muted);
  font-family: Arial, Helvetica, sans-serif;
  font-size: 13px;
}

.cite-ref, .equation-ref, .table-ref, .figure-ref, .section-ref {
  font-family: inherit;
}

.missing-ref {
  color: #9a3412;
}

.table-wrap {
  overflow-x: auto;
  margin: 24px 0;
}

table {
  width: 100%;
  border-collapse: collapse;
  background: var(--paper);
  font-family: Arial, Helvetica, sans-serif;
  font-size: 14px;
}

th, td {
  padding: 10px 12px;
  border: 1px solid var(--line);
  text-align: left;
  vertical-align: top;
}

.caption {
  margin-top: 8px;
  color: var(--muted);
  font-family: Arial, Helvetica, sans-serif;
  font-size: 13px;
}

.note-figure {
  margin: 24px 0;
  padding: 0;
}

.note-figure img {
  display: block;
  max-width: 100%;
  height: auto;
  border: 1px solid var(--line);
  border-radius: 4px;
  background: var(--paper);
}

.page-nav {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  gap: 12px;
  margin-top: 36px;
  padding-top: 20px;
  border-top: 1px solid var(--line);
  font-family: Arial, Helvetica, sans-serif;
  font-size: 14px;
}

.page-nav a { display: inline-flex; align-items: center; }
.page-nav .index-link { justify-content: center; }
.page-nav .next-link { justify-content: flex-end; }

.program-footer {
  margin-top: 28px;
  color: var(--muted);
  font-family: Arial, Helvetica, sans-serif;
  font-size: 13px;
  text-align: center;
}

code {
  font-family: "Courier New", monospace;
  font-size: 0.95em;
}

@media (max-width: 720px) {
  body { font-size: 17px; }
  .page { padding: 28px 18px 52px; }
  h1 { font-size: 34px; }
  .question { font-size: 22px; }
  .program-grid { grid-template-columns: 1fr; }
  .page-nav { grid-template-columns: 1fr; }
  .page-nav .index-link, .page-nav .next-link { justify-content: flex-start; }
}