:root {
  color-scheme: light dark;
  --background: #fbfaf7;
  --surface: #ffffff;
  --text: #202124;
  --muted: #555b63;
  --accent: #174ea6;
  --accent-visited: #6a2781;
  --border: #c8ccd0;
  --focus: #b24b00;
  --code: #f0f2f4;
  font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  line-height: 1.65;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body { margin: 0; background: var(--background); color: var(--text); }
a { color: var(--accent); text-underline-offset: 0.16em; }
a:visited { color: var(--accent-visited); }
a:hover { text-decoration-thickness: 0.16em; }
a:focus-visible, [tabindex="-1"]:focus-visible { outline: 0.2rem solid var(--focus); outline-offset: 0.2rem; }
.skip-link { position: absolute; top: -5rem; left: 1rem; z-index: 10; padding: 0.75rem 1rem; background: var(--surface); color: var(--text); }
.skip-link:focus { top: 1rem; }
.site-header { border-bottom: 1px solid var(--border); background: var(--surface); }
.site-header__inner { display: flex; align-items: center; justify-content: space-between; gap: 1.5rem; max-width: 76rem; margin: 0 auto; padding: 1rem 1.25rem; }
.site-title { color: var(--text); font-weight: 750; text-decoration: none; }
.site-header nav { display: flex; flex-wrap: wrap; gap: 0.5rem 1.25rem; }
main { max-width: 76rem; min-height: 70vh; margin: 0 auto; padding: 2rem 1.25rem 4rem; }
.hero, .course-index, .page-shell, .lesson { max-width: 72ch; margin-inline: auto; }
.hero { padding-block: 2rem; }
.eyebrow { color: var(--muted); font-size: 0.88rem; font-weight: 700; letter-spacing: 0.06em; text-transform: uppercase; }
.hero-figure { margin: 2rem 0 0; }
.hero-figure img { display: block; width: 100%; height: auto; border: 1px solid var(--border); border-radius: 0.25rem; }
.hero-figure figcaption { margin-top: 0.5rem; color: var(--muted); font-size: 0.92rem; }
h1, h2, h3, h4 { line-height: 1.2; scroll-margin-top: 1rem; }
h1 { font-size: clamp(2rem, 5vw, 3.25rem); }
h2 { margin-top: 2.25rem; }
p, li { max-width: 72ch; }
.course-list { padding-left: 1.5rem; }
.course-list li { margin-block: 0.85rem; padding-left: 0.5rem; }
.course-list a { display: block; font-weight: 700; }
.course-list span { display: block; color: var(--muted); font-size: 0.92rem; }
.breadcrumb { display: flex; flex-wrap: wrap; gap: 0.5rem; margin-bottom: 1.5rem; color: var(--muted); }
.lesson-summary { margin-block: 1.5rem 2.5rem; padding: 0.5rem 1.25rem 1.25rem; border: 1px solid var(--border); border-left: 0.35rem solid var(--accent); border-radius: 0.25rem; background: var(--surface); }
.lesson-summary__title { margin: 0.75rem 0 0.5rem; font-size: 1.5rem; font-weight: 750; line-height: 1.2; }
.lesson-summary__label { margin: 0.75rem 0 0.25rem; font-weight: 700; }
.lesson-summary ul { margin-top: 0.25rem; }
.lesson-content img { display: block; max-width: 100%; height: auto; margin-inline: auto; border: 1px solid var(--border); background: #fff; }
.lesson-content pre { max-width: 100%; overflow-x: auto; padding: 1rem; border: 1px solid var(--border); border-radius: 0.25rem; background: var(--code); }
.lesson-content code { padding: 0.08em 0.2em; border-radius: 0.2rem; background: var(--code); font-family: ui-monospace, "Cascadia Code", "SFMono-Regular", Consolas, monospace; font-size: 0.92em; }
.lesson-content pre code { padding: 0; background: transparent; }
.lesson-content blockquote { margin-inline: 0; padding-left: 1rem; border-left: 0.3rem solid var(--border); color: var(--muted); }
.lesson-content table { display: block; max-width: 100%; overflow-x: auto; border-collapse: collapse; }
th, td { padding: 0.5rem; border: 1px solid var(--border); text-align: left; vertical-align: top; }
.lesson-pagination { display: grid; grid-template-columns: 1fr 1fr; gap: 1rem; margin-top: 3rem; padding-top: 1.25rem; border-top: 1px solid var(--border); }
.lesson-pagination div:last-child { text-align: right; }
.lesson-pagination span, .lesson-pagination a { display: block; }
.lesson-pagination span { color: var(--muted); font-size: 0.85rem; }
.site-footer { padding: 1.5rem; border-top: 1px solid var(--border); background: var(--surface); color: var(--muted); }
.site-footer p { margin: 0 auto; }

@media (max-width: 42rem) {
  .site-header__inner { align-items: flex-start; flex-direction: column; }
  .lesson-pagination { grid-template-columns: 1fr; }
  .lesson-pagination div:last-child { text-align: left; }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { animation-duration: 0.01ms !important; animation-iteration-count: 1 !important; transition-duration: 0.01ms !important; }
}

@media (prefers-color-scheme: dark) {
  :root { --background: #151719; --surface: #202327; --text: #f2f3f4; --muted: #c1c6cc; --accent: #8ab4f8; --accent-visited: #d7a8e8; --border: #5f666e; --focus: #ffad66; --code: #292d32; }
}

@media print {
  .skip-link, .site-header, .lesson-pagination { display: none; }
  body, main { max-width: none; padding: 0; background: #fff; color: #000; }
  a { color: #000; }
  a[href]::after { content: " (" attr(href) ")"; overflow-wrap: anywhere; font-size: 0.8em; }
}