.skip-link { position: fixed; top: 8px; left: 16px; z-index: 30; padding: 10px 16px; background: var(--ink); color: white; transform: translateY(-160%); }
.skip-link:focus { transform: none; }
.lesson-breadcrumb { display: flex; flex-wrap: wrap; gap: 10px; padding: 28px 0; color: var(--muted); font-size: 13px; }
.lesson-breadcrumb a:hover { color: var(--green); text-decoration: underline; }
.lesson-layout { display: grid; grid-template-columns: 210px minmax(0, 1fr); gap: 64px; align-items: start; }
.lesson-sidebar { position: sticky; top: 116px; max-height: calc(100vh - 144px); overflow-y: auto; padding-bottom: 8px; }
.lesson-toc summary { display: flex; align-items: baseline; justify-content: space-between; padding: 8px 0 16px; border-bottom: 1px solid var(--line); font-size: 14px; font-weight: 600; list-style: none; }
.lesson-toc summary::-webkit-details-marker { display: none; }
.lesson-toc summary span { font-size: 11px; font-weight: 400; color: var(--muted); }
.lesson-toc ol { list-style: none; margin: 12px 0 24px; padding: 0; }
.lesson-toc li + li { margin-top: 4px; }
.lesson-toc a { display: flex; gap: 9px; padding: 9px 10px; border-radius: 3px; color: var(--muted); font-size: 13px; line-height: 1.6; }
.lesson-toc a:hover, .lesson-toc a[aria-current="location"] { background: var(--green-soft); color: var(--ink); }
.toc-number { width: 17px; flex-shrink: 0; font-variant-numeric: tabular-nums; color: var(--green); }
.back-to-course { display: block; padding: 16px 0 0; border-top: 1px solid var(--line); color: var(--muted); font-size: 12px; }
.lesson-reading { min-width: 0; max-width: 800px; }
.lesson-heading { padding: 0 0 28px; margin-bottom: 28px; border-bottom: 1px solid var(--line); }
.lesson-heading .eyebrow { margin-bottom: 12px; }
.lesson-heading h1 { font-size: clamp(34px, 4.3vw, 48px); font-weight: 500; letter-spacing: -.045em; margin-bottom: 7px; }
.lesson-subtitle { color: var(--muted); font-size: 18px; margin-bottom: 22px; }
.lesson-meta { display: flex; align-items: center; flex-wrap: wrap; gap: 8px 20px; color: var(--muted); font-size: 12px; }
.print-lesson { margin-left: auto; padding: 3px 0; border: 0; border-bottom: 1px solid var(--line); background: none; font-size: 12px; }
.print-lesson:hover { color: var(--green); border-color: var(--green); }
.lesson-content { line-height: 1.85; font-size: 16px; overflow-wrap: break-word; }
.lesson-content h2 { margin: 60px 0 22px; padding-top: 28px; border-top: 1px solid var(--line); font-size: 27px; line-height: 1.35; letter-spacing: -.03em; scroll-margin-top: 116px; }
.lesson-content h2:first-of-type { margin-top: 40px; }
.lesson-content h3 { margin: 30px 0 12px; font-size: 19px; line-height: 1.5; letter-spacing: -.015em; }
.lesson-content h2 + h3 { color: var(--green); font-size: 17px; font-weight: 400; margin-top: -8px; margin-bottom: 24px; }
.lesson-content p { margin-bottom: 16px; }
.lesson-content ul, .lesson-content ol { margin: 12px 0 22px; padding-left: 24px; }
.lesson-content li + li { margin-top: 6px; }
.lesson-content strong { font-weight: 600; }
.lesson-content a, .lesson-credits a { color: var(--green); text-decoration: underline; text-underline-offset: 3px; text-decoration-thickness: 1px; }
.lesson-content code { background: var(--paper); border: 1px solid var(--line); padding: 1px 5px; border-radius: 3px; font-size: .88em; }
.math-block { display: block; max-width: 100%; overflow-x: auto; overflow-y: hidden; padding: 4px 0; }
.lesson-content mjx-container[display="true"] { margin: .8em 0 !important; }
.lesson-table { max-width: 100%; overflow-x: auto; margin: 22px 0 28px; border: 1px solid var(--line); border-radius: 3px; }
.lesson-table table { width: 100%; min-width: 420px; border-collapse: collapse; line-height: 1.6; font-size: 14px; }
.lesson-table th, .lesson-table td { padding: 11px 13px; border-bottom: 1px solid var(--line); vertical-align: top; }
.lesson-table th { text-align: left; background: var(--paper); font-weight: 600; }
.lesson-table tbody tr:last-child td { border-bottom: 0; }
.lesson-table td + td, .lesson-table th + th { border-left: 1px solid var(--line); }
.lesson-figure { margin: 30px 0; padding: 22px 14px 15px; border: 1px solid var(--line); border-radius: 3px; background: white; }
.lesson-figure a { display: block; }
.lesson-figure img { display: block; width: 100%; height: auto; margin-inline: auto; }
.lesson-figure figcaption { margin: 16px 5px 0; color: var(--muted); font-size: 12px; line-height: 1.6; }
.lesson-figure figcaption span { color: var(--green); margin-right: 8px; font-weight: 600; }
.lesson-callout { margin: 24px 0; padding: 18px 22px; background: var(--green-soft); border-left: 3px solid #99a58e; border-radius: 0 3px 3px 0; font-size: 15px; }
.lesson-callout.callout-warning { background: var(--yellow-soft); border-left-color: var(--yellow); }
.lesson-callout .callout-title { margin: 0 0 7px; font-weight: 600; }
.lesson-callout > :last-child { margin-bottom: 0; }
.lesson-example { margin: 30px 0; padding: 24px 26px; background: var(--paper); border: 1px solid var(--line); border-radius: 4px; }
.lesson-example h3 { margin: 0 0 20px; color: var(--ink); font-size: 18px; }
.lesson-example h3::before { content: ""; display: inline-block; width: 7px; height: 7px; background: #a4b197; margin: 0 9px 3px 0; }
.lesson-example > :last-child { margin-bottom: 0; }
.lesson-example p { font-size: 15px; }
.lesson-disclosure { margin: 22px 0; border: 1px solid var(--line); border-radius: 3px; font-size: 14px; }
.lesson-disclosure summary { padding: 16px 20px; font-weight: 500; line-height: 1.65; }
.lesson-disclosure summary::marker { color: var(--green); }
.lesson-disclosure summary span { margin-left: 8px; font-size: 12px; color: var(--muted); }
.lesson-disclosure[open] summary { border-bottom: 1px solid var(--line); background: var(--paper); }
.disclosure-body { padding: 20px 22px; }
.disclosure-body > :last-child { margin-bottom: 0; }
.answer-disclosure { border-color: #c8d3bf; }
.answer-disclosure summary { background: var(--green-soft); }
.lesson-credits { margin-top: 40px; padding-top: 24px; border-top: 1px solid var(--line); font-size: 12px; line-height: 1.8; color: var(--muted); }
.credits-title { font-weight: 600; margin-bottom: 6px; }
.lesson-end { display: grid; grid-template-columns: 1fr 1fr; gap: 28px; margin-top: 30px; padding: 26px 0; border-top: 1px solid var(--line); border-bottom: 1px solid var(--line); }
.lesson-end span, .lesson-end strong, .lesson-end small { display: block; }
.lesson-end span, .lesson-end small { color: var(--muted); font-size: 12px; font-weight: 400; }
.lesson-end strong { margin-top: 5px; font-size: 15px; font-weight: 500; }
.lesson-end small { margin-top: 5px; }
.lesson-end p { margin: 0; }
.lesson-end a:hover strong { color: var(--green); }
.lesson-top { display: block; margin: 22px 0 0; color: var(--muted); font-size: 12px; text-align: right; }
.lesson-related { margin: 16px 0 0; color: var(--muted); font-size: 12px; }
.lesson-related-links { margin-top: 36px; padding-top: 24px; border-top: 1px solid var(--line); font-size: 14px; }
.lesson-related-links h2 { font-size: 16px; margin-bottom: 14px; }
.lesson-related-links ul { padding-left: 20px; }
.lesson-related-links li + li { margin-top: 8px; }
.lesson-related-links a { color: var(--green); text-decoration: underline; text-underline-offset: 3px; }
.lesson-portrait { margin: 8px 0 18px; }
.lesson-portrait img { display: block; width: 100%; height: auto; border-radius: 3px; }
.history .disclosure-body { display: flow-root; }
.history .lesson-portrait { float: right; margin: 3px 0 16px 24px; max-width: 35%; }
.lesson-portrait-pair { display: flex; justify-content: center; align-items: start; gap: 24px; margin: 8px 0 22px; }
.history .lesson-portrait-pair .lesson-portrait { float: none; margin: 0; max-width: calc(50% - 12px); }
.lesson-content h4 { font-size: 17px; line-height: 1.5; margin: 26px 0 12px; font-weight: 600; }
.lesson-content h5 { font-size: 16px; margin: 22px 0 12px; }
.lesson-credits li + li { margin-top: 6px; }
@media (max-width: 1050px) { .lesson-layout { grid-template-columns: 186px minmax(0, 1fr); gap: 36px; } }
@media (max-width: 760px) {
  .lesson-breadcrumb { padding: 22px 0; font-size: 12px; }
  .lesson-layout { display: flex; flex-direction: column; gap: 24px; }
  .lesson-sidebar { position: static; max-height: none; width: 100%; padding: 0; }
  .lesson-toc { border: 1px solid var(--line); border-radius: 3px; background: var(--paper); }
  .lesson-toc summary { padding: 12px 16px; border-bottom: 0; }
  .lesson-toc summary::after { content: "+"; margin-left: auto; color: var(--green); }
  .lesson-toc[open] summary::after { content: "−"; }
  .lesson-toc summary span { margin-left: 12px; }
  .lesson-toc ol { display: grid; grid-template-columns: 1fr 1fr; margin: 0; padding: 0 6px 10px; gap: 2px; }
  .lesson-toc li + li { margin-top: 0; }
  .lesson-toc a { font-size: 12px; padding: 8px; gap: 4px; }
  .back-to-course { display: none; }
  .lesson-reading { width: 100%; }
  .lesson-heading { margin-bottom: 24px; padding-bottom: 22px; }
  .lesson-content h2 { margin-top: 46px; padding-top: 24px; font-size: 24px; scroll-margin-top: 148px; }
  .lesson-content h3 { font-size: 18px; }
  .lesson-example { padding: 20px 17px; }
  .lesson-callout { padding: 16px 17px; }
  .lesson-figure { padding: 14px 8px; }
  .disclosure-body { padding: 17px; }
  .lesson-disclosure summary { padding: 14px 17px; }
  .lesson-end { gap: 20px; }
}
@media (max-width: 400px) { .lesson-meta { gap: 8px 12px; } .print-lesson { margin-left: 0; } .lesson-end { grid-template-columns: 1fr; } }
@media print {
  @page { size: A4; margin: 15mm; }
  .site-header, .site-footer, .lesson-sidebar, .lesson-breadcrumb, .print-lesson, .lesson-end, .lesson-top, .skip-link { display: none !important; }
  main.lesson-main { width: 100%; padding: 0; }
  .lesson-layout { display: block; }
  .lesson-reading { max-width: none; }
  .lesson-content { font-size: 10.5pt; line-height: 1.65; }
  .lesson-content h2 { font-size: 18pt; break-after: avoid; }
  .lesson-content h3 { font-size: 13pt; break-after: avoid; }
  .lesson-example p, .lesson-callout { font-size: 10.5pt; }
  .lesson-heading { margin-bottom: 18px; padding-bottom: 18px; }
  .lesson-figure { break-inside: avoid; }
  .lesson-figure img { max-height: 120mm; object-fit: contain; }
  .lesson-table { overflow: visible; }
  .lesson-table table { min-width: 0; font-size: 9pt; }
  .lesson-table th, .lesson-table td { padding: 7px; }
  .lesson-table tr { break-inside: avoid; }
  .lesson-example { background: none; }
  .lesson-disclosure { break-inside: auto; }
  .lesson-disclosure:not([open]) { display: none; }
  .math-block { overflow: visible; }
}