/* Persistent chapter navigation beside the reading column; a sticky menu on smaller screens. */
.learn-layout { display: grid; grid-template-columns: 248px minmax(0, 1fr); align-items: start; gap: 48px; width: calc(100% - 2 * var(--page-padding)); max-width: var(--page-width); margin: 0 auto; }
.article { padding: 72px 0 96px; min-width: 0; outline: none; }
.overview-article { padding-top: 80px; }
.course-sidebar { position: sticky; top: 96px; margin-top: 72px; max-height: calc(100dvh - 120px); overflow-y: auto; overscroll-behavior: contain; scrollbar-width: thin; padding: 0 20px 16px 0; border-right: 1px solid var(--line-soft); }
.sidebar-heading { padding: 0 10px 20px; }
.sidebar-heading p { margin: 0 0 7px; color: var(--muted); font-size: 12px; }
.sidebar-heading h2 { margin: 0; color: var(--heading); font-size: 16px; font-weight: 600; }
.course-chapters { display: grid; gap: 4px; }
.course-chapters > a { display: flex; align-items: baseline; gap: 10px; padding: 10px; border-radius: 6px; color: var(--text); font-size: 13px; line-height: 1.7; }
.course-chapters > a:hover { background: var(--surface); color: var(--heading); text-decoration: none; }
.course-chapters > a[aria-current], .sidebar-resources > a[aria-current] { background: var(--accent-soft); color: var(--accent); font-weight: 500; }
.course-chapters > a[aria-current] .lesson-index { color: inherit; }
.course-chapters .lesson-index { min-width: 22px; }
.course-chapters .icon { display: none; }
.sidebar-resources { display: grid; gap: 4px; margin-top: 16px; padding-top: 16px; border-top: 1px solid var(--line-soft); }
.sidebar-resources > a { display: flex; align-items: center; gap: 10px; padding: 8px 10px; border-radius: 6px; color: var(--muted); font-size: 12px; }
.sidebar-resources .icon { width: 16px; height: 16px; }
.sidebar-page-toc { border-top: 1px solid var(--line-soft); margin-top: 16px; padding-top: 16px; }
.sidebar-page-toc summary { padding: 0 10px; cursor: pointer; color: var(--muted); font-size: 12px; }
.sidebar-page-toc nav { display: grid; gap: 4px; padding-top: 12px; }
.sidebar-page-toc a { padding: 6px 10px; color: var(--text); font-size: 12px; overflow-wrap: anywhere; }
.page-contents { display: none; position: sticky; top: 96px; margin-top: 72px; max-height: calc(100dvh - 120px); overflow-y: auto; overscroll-behavior: contain; scrollbar-width: thin; padding-bottom: 20px; }
.page-contents h2 { margin: 0 0 16px; padding-left: 12px; color: var(--muted); font-size: 12px; font-weight: 500; }
.page-links { display: grid; gap: 4px; }
.page-links a { display: block; padding: 7px 12px; border-left: 1px solid var(--line); color: var(--muted); font-size: 12px; line-height: 1.8; overflow-wrap: anywhere; }
.page-links a:hover { color: var(--heading); background: var(--surface); text-decoration: none; }
[data-page-toc] a[aria-current="location"] { color: var(--accent); }
.page-links a[aria-current="location"] { border-left-color: var(--accent); background: var(--accent-soft); }
.back-to-top { display: inline-flex; gap: 10px; margin: 22px 12px 0; color: var(--muted); font-size: 12px; }
.chapter-header { margin-bottom: 42px; }
.breadcrumb { display: flex; flex-wrap: wrap; gap: 12px; align-items: center; margin-bottom: 25px; color: var(--muted); font-size: 13px; }
.breadcrumb a { color: var(--muted); }
.breadcrumb > span:nth-child(2) { color: var(--line); }
h1 { font-size: 38px; line-height: 1.4; letter-spacing: -.035em; font-weight: 650; color: var(--heading); margin: 0 0 23px; }
.overview-article h1 { font-size: 48px; letter-spacing: -.04em; }
.lede { max-width: 1040px; margin: 0; color: var(--muted); font-size: 17px; line-height: 1.95; }
.hero-actions { display: flex; gap: 26px; align-items: center; flex-wrap: wrap; margin-top: 32px; }
.primary-action, .text-action { display: inline-flex; align-items: center; gap: 12px; font-size: 14px; }
.text-action { color: var(--text); }
.course-meta { font-size: 12px; color: var(--muted); margin: 24px 0 0; }
.course-meta span { margin: 0 12px; }
.overview-nav { display: flex; align-items: baseline; gap: 12px 32px; padding: 16px 0; margin-bottom: 42px; border-block: 1px solid var(--line-soft); }
.overview-nav-label { flex-shrink: 0; color: var(--muted); font-size: 12px; }
.overview-nav-links { display: flex; flex-wrap: wrap; gap: 8px 28px; }
.overview-nav-links a { padding-block: 5px; color: var(--text); font-size: 13px; }
.overview-nav-links a:hover { color: var(--accent); }
.overview-nav-links a:last-child { color: var(--accent); }
.chapter-toc { border-block: 1px solid var(--line-soft); margin: 0 0 42px; padding: 14px 0; font-size: 13px; }
.chapter-toc summary { cursor: pointer; width: fit-content; color: var(--muted); }
.chapter-toc nav { display: grid; gap: 9px; padding: 18px 0 5px 17px; }
.chapter-toc a { color: var(--text); }
.chapter-number { font: 11px/1.7 var(--mono); margin-left: auto; }

.prose { font-size: 16px; line-height: 1.95; }
.prose h2, .syllabus h2 { margin: 62px 0 22px; padding-top: 28px; border-top: 1px solid var(--line-soft); font-size: 25px; line-height: 1.5; letter-spacing: -.02em; color: var(--heading); font-weight: 600; }
.prose h2:first-child { margin-top: 0; padding-top: 0; border: 0; }
.prose h3 { font-size: 19px; line-height: 1.65; color: var(--heading); font-weight: 600; margin: 32px 0 14px; }
.prose p { max-width: 1120px; margin: 18px 0; }
.prose strong { color: var(--heading); font-weight: 600; }
.prose :where(ul, ol) { padding-left: 24px; }
.prose li { padding-left: 3px; margin: 9px 0; }
.prose p a:not(.download), .prose li a { text-decoration: underline; text-decoration-color: var(--line); text-underline-offset: 4px; }
.prose code:not(pre code), .lede code { font: .88em/1.6 var(--mono); color: var(--heading); background: var(--raised); padding: 2px 5px; border-radius: 4px; overflow-wrap: anywhere; }
.file-link { font: 12px/1.7 var(--mono); overflow-wrap: anywhere; }
.note { padding: 3px 0 3px 20px; margin: 30px 0; border-left: 2px solid var(--line); }
.note > strong { color: var(--heading); font-size: 14px; }
.note p { margin: 5px 0 0; color: var(--muted); font-size: 14px; }
.download { display: inline-flex; align-items: center; gap: 16px; padding: 10px 17px; margin: 4px 15px 4px 0; border: 1px solid var(--line); border-radius: 6px; color: var(--heading); font-size: 13px; }
.download:hover { background: var(--surface); text-decoration: none; }
.download span { color: var(--muted); font: 11px/1.6 var(--mono); }
.lesson-goals { margin: 0 0 35px; }
.lesson-goals > p { color: var(--heading); font-size: 14px; font-weight: 600; }
.lesson-goals ul { color: var(--muted); font-size: 14px; }

/* Theme-aware code. Only the lines currently being explained receive emphasis. */
.code-block { margin: 25px 0 28px; border: 1px solid var(--line); border-radius: 8px; background: var(--bg); overflow: hidden; min-width: 0; }
.code-block figcaption { display: flex; align-items: center; gap: 12px; padding: 9px 16px; min-height: 43px; background: var(--surface); border-bottom: 1px solid var(--line-soft); color: var(--muted); font: 11px/1.7 var(--mono); }
.code-block figcaption .file-link { color: var(--text); font-size: 12px; }
.code-block figcaption > span { white-space: nowrap; }
.copy { display: inline-flex; align-items: center; gap: 5px; padding: 4px 6px; min-height: 26px; margin-left: auto; border: 0; border-radius: 4px; color: var(--muted); background: transparent; font: 11px/1.6 var(--sans); flex: 0 0 auto; }
.copy:hover { background: var(--raised); color: var(--heading); }
.copy .icon { width: 14px; height: 14px; }
pre { font: 13px/1.9 var(--mono); color: var(--code-text); margin: 0; padding: 20px 22px; overflow: auto; tab-size: 4; }
pre code { font: inherit; white-space: pre; }
.code-line { display: inline-block; min-width: 100%; }
.source-line { min-height: 1.9em; vertical-align: top; scroll-margin-top: 16px; }
.source-line:target { background: var(--highlight); box-shadow: -22px 0 var(--highlight), 22px 0 var(--highlight); }
.code-line.highlighted { background: var(--highlight); box-shadow: -22px 0 var(--highlight), 22px 0 var(--highlight); position: relative; }
.code-line.highlighted::before { content: ""; position: absolute; left: -22px; top: 0; bottom: 0; border-left: 2px solid var(--highlight-line); }
.terminal-label { display: inline-flex; align-items: center; gap: 10px; font-family: var(--sans); }
.terminal-label > span { color: var(--muted); font-family: var(--mono); }
.terminal pre, .output pre { background: var(--surface); }
.output-label { font-family: var(--sans); }
.output figcaption { background: var(--bg); }
.syntax-keyword { color: var(--code-keyword); }
.syntax-string { color: var(--code-string); }
.syntax-comment { color: var(--code-comment); }
.syntax-literal { color: var(--code-literal); }
.syntax-type, .syntax-function { color: var(--code-function); }

/* A real service contract, rather than a fictional dashboard, introduces the result. */
.project-preview { border: 1px solid var(--line); border-radius: 10px; margin: 28px 0 24px; overflow: hidden; }
.preview-heading { display: flex; align-items: center; gap: 9px; justify-content: space-between; padding: 16px 22px; border-bottom: 1px solid var(--line); font-size: 13px; color: var(--heading); }
.preview-heading > span { display: inline-flex; align-items: center; gap: 9px; }
.preview-dot { width: 7px; height: 7px; background: var(--accent); border-radius: 50%; }
.preview-heading > code { color: var(--muted) !important; font-size: 11px !important; background: transparent !important; }
.preview-columns { display: grid; grid-template-columns: 1fr 1.2fr; }
.preview-columns > div { padding: 24px; min-width: 0; }
.preview-columns > div + div { border-left: 1px solid var(--line); background: var(--surface); }
.preview-label { font-size: 12px; color: var(--muted); margin-bottom: 12px; }
.request-line { display: flex; align-items: baseline; gap: 10px; font: 13px/1.8 var(--mono); color: var(--heading); }
.request-line span { color: var(--accent); }
.preview-columns pre { padding: 16px 0 0; font-size: 13px; }
.preview-caption { border-top: 1px solid var(--line); padding: 13px 22px; color: var(--muted); font-size: 12px; line-height: 1.8; }
.project-results { display: grid; grid-template-columns: repeat(3, 1fr); gap: 28px; list-style: none; padding: 0 !important; margin: 30px 0 44px; }
.project-results li { margin: 0; padding: 0; }
.project-results b { display: block; color: var(--heading); font-weight: 600; font-size: 14px; margin-bottom: 5px; }
.project-results span { display: block; color: var(--muted); font-size: 13px; line-height: 1.9; }
.section-eyebrow { font-size: 12px; color: var(--muted); margin-top: 72px; }
.syllabus h2 { border: 0; margin: 8px 0 24px; padding: 0; font-size: 29px; }

.table-wrap { overflow: auto; margin: 26px 0; }
table { width: 100%; border-collapse: collapse; min-width: 460px; font-size: 14px; line-height: 1.9; }
td, th { padding: 13px 15px; border-bottom: 1px solid var(--line); vertical-align: top; text-align: left; }
th { background: var(--surface); color: var(--heading); font-weight: 500; font-size: 12px; border-top: 1px solid var(--line); }
td:first-child { color: var(--heading); }
td .file-link { font-size: 11px; }
.flow { display: flex; gap: 9px; align-items: stretch; flex-wrap: wrap; margin: 30px 0; }
.flow > div { flex: 1; min-width: 120px; padding: 15px 13px; border: 1px solid var(--line); border-radius: 5px; }
.flow b { display: block; color: var(--heading); font: 500 13px/1.8 var(--mono); }
.flow span { font-size: 12px; color: var(--muted); }
.flow > i { align-self: center; font-style: normal; color: var(--muted); }
.flow > .focus { background: var(--surface); }
.request-trace { list-style: none; padding: 0 !important; margin: 30px 0; counter-reset: trace; }
.request-trace > li { display: grid; grid-template-columns: 28px 1fr; gap: 13px; margin: 0; padding: 19px 0; border-bottom: 1px solid var(--line-soft); }
.request-trace > li::before { counter-increment: trace; content: counter(trace, decimal-leading-zero); font: 12px/2 var(--mono); color: var(--muted); }
.request-trace strong { display: block; font-size: 15px; }
.request-trace p { margin: 6px 0 0; font-size: 14px; color: var(--muted); }
.request-trace .file-link { font-size: 11px; }
.checkpoint { margin: 30px 0; padding: 20px 23px; border: 1px solid var(--line); border-radius: 8px; }
.checkpoint > strong { font-size: 14px; }
.checkpoint p { margin: 8px 0 0; font-size: 14px; }
.answer { border-block: 1px solid var(--line); padding: 16px 0; margin: 25px 0; }
.answer summary { color: var(--heading); font-size: 14px; cursor: pointer; }
.answer[open] summary { margin-bottom: 20px; }
.answer p { font-size: 14px; }
.pagination { display: grid; grid-template-columns: 1fr 1fr; gap: 30px; border-top: 1px solid var(--line); padding-top: 28px; margin-top: 72px; }
.pagination a { display: flex; flex-direction: column; align-items: flex-start; gap: 8px; color: var(--heading); font-size: 14px; }
.pagination a:last-child { align-items: flex-end; text-align: right; }
.pagination small { color: var(--muted); font-size: 12px; }
.doc-footer { display: flex; align-items: center; justify-content: space-between; gap: 20px; margin-top: 45px; padding-top: 25px; border-top: 1px solid var(--line-soft); font-size: 12px; color: var(--muted); }
.doc-footer a { display: flex; gap: 8px; align-items: center; color: var(--muted); }
.doc-footer .icon { width: 14px; height: 14px; }

/* Native dialog supplies focus trapping and Escape handling at every viewport. */
.reading-dock { display: none; align-items: center; gap: 20px; position: sticky; z-index: 25; top: 73px; min-height: 64px; padding: 10px var(--page-padding); border-bottom: 1px solid var(--line); background: var(--bg); }
.contents-toggle, .page-contents-toggle { display: flex; align-items: center; gap: 9px; flex-shrink: 0; background: transparent; color: var(--heading); border: 0; border-radius: 5px; padding: 9px 12px; font-size: 13px; }
.contents-toggle:hover, .page-contents-toggle:hover { background: var(--surface); }
.dock-current { flex: 1; border-left: 1px solid var(--line); padding-left: 20px; min-width: 0; line-height: 1.6; }
.dock-current > span { color: var(--muted); display: block; font-size: 10px; }
.dock-current > strong { display: block; font-size: 13px; font-weight: 500; color: var(--heading); white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.dock-next { display: flex; align-items: center; gap: 10px; font-size: 13px; color: var(--heading); margin-left: auto; flex-shrink: 0; padding: 7px 9px; }
.contents-dialog, .page-dialog { width: min(640px, calc(100% - 32px)); max-height: calc(100dvh - 80px); margin: auto; padding: 0; border: 1px solid var(--line); border-radius: 12px; background: var(--bg); color: var(--text); box-shadow: 0 24px 100px #0002; overscroll-behavior: contain; }
.contents-dialog::backdrop, .page-dialog::backdrop { background: #0005; backdrop-filter: blur(3px); }
body:has(.contents-dialog[open], .page-dialog[open]) { overflow: hidden; }
.page-dialog .page-links { padding: 20px 30px 28px; }
.page-dialog .page-links a { font-size: 14px; padding-block: 10px; }
.contents-heading { display: flex; justify-content: space-between; align-items: center; gap: 20px; padding: 24px 30px; border-bottom: 1px solid var(--line); }
.contents-dialog .contents-heading, .page-dialog .contents-heading { position: sticky; top: 0; z-index: 1; background: var(--bg); }
.contents-heading p { font-size: 12px; color: var(--muted); margin: 0 0 6px; }
.contents-heading h2 { font-size: 22px; font-weight: 600; color: var(--heading); margin: 0; }
.close-contents, .close-page-contents { display: grid; place-items: center; flex-shrink: 0; font-size: 26px; font-weight: 300; color: var(--muted); background: none; border: 0; border-radius: 5px; width: 36px; height: 36px; }
.close-contents:hover, .close-page-contents:hover { background: var(--surface); }
.chapter-list { display: grid; }
.chapter-list > a { display: flex; align-items: center; gap: 20px; color: var(--heading); border-bottom: 1px solid var(--line-soft); padding: 19px 0; font-size: 15px; }
.chapter-list > a:hover { color: var(--accent); text-decoration: none; }
.chapter-list > a > .icon { margin-left: auto; width: 16px; height: 16px; color: var(--muted); }
.lesson-index { color: var(--muted); font: 12px/1.8 var(--mono); min-width: 25px; }
.chapter-list strong { display: block; font-size: 16px; font-weight: 500; }
.chapter-list small { display: block; color: var(--muted); font-size: 13px; margin-top: 5px; }
.contents-dialog .chapter-list { padding: 12px 20px; }
.contents-dialog .chapter-list > a { padding: 11px 12px; border: 0; border-radius: 5px; gap: 16px; font-size: 14px; }
.contents-dialog .chapter-list > a:hover { background: var(--surface); }
.contents-dialog .chapter-list > a[aria-current] { background: var(--accent-soft); color: var(--accent); }
.contents-dialog [aria-current] .lesson-index { color: var(--accent); }
.contents-footer { display: flex; align-items: center; flex-wrap: wrap; gap: 20px; padding: 20px 30px; border-top: 1px solid var(--line); font-size: 12px; }
.contents-footer a { display: flex; align-items: center; gap: 7px; color: var(--text); }
.contents-footer > span { color: var(--muted); margin-left: auto; font-size: 10px; }
.contents-footer .icon { width: 15px; height: 15px; }
.toast { position: fixed; z-index: 40; bottom: 24px; left: 50%; transform: translateX(-50%); width: max-content; max-width: calc(100% - 32px); padding: 11px 18px; border: 1px solid var(--line); border-radius: 7px; background: var(--heading); color: var(--bg); font-size: 13px; opacity: 0; pointer-events: none; transition: opacity .15s; }
.toast.visible { opacity: 1; }
.source-index { display: grid; gap: 8px; padding: 24px; margin: 28px 0 50px; background: var(--surface); border: 1px solid var(--line); border-radius: 8px; }
.source-index a { font: 12px/1.9 var(--mono); overflow-wrap: anywhere; }
.source-file { scroll-margin-top: 16px; }
.source-file h2 { margin-top: 48px; color: var(--heading); font: 16px/1.7 var(--mono); overflow-wrap: anywhere; }
.source-file:target h2 { color: var(--accent); }

@media (min-width: 1480px) {
  .learn { --page-width: 1600px; }
  .learn-layout { grid-template-columns: 224px minmax(0, 1fr) 200px; gap: 32px; }
  .page-contents { display: block; }
  .sidebar-page-toc { display: none; }
}
@media (max-width: 1100px) {
  html:has(.learn-layout) { scroll-padding-top: 160px; }
  .learn-layout { display: block; }
  .course-sidebar { display: none; position: static; max-height: none; margin-top: 32px; padding-right: 0; border-right: 0; border-bottom: 1px solid var(--line-soft); }
  .reading-dock { display: flex; }
}
@media (max-width: 640px) {
  html:has(.learn-layout) { scroll-padding-top: 192px; }
  .article { padding-top: 40px; padding-bottom: 72px; }
  .chapter-header { margin-bottom: 30px; }
  .breadcrumb { margin-bottom: 20px; font-size: 12px; gap: 9px; }
  h1, .overview-article h1 { font-size: 31px; letter-spacing: -.035em; }
  .lede { font-size: 15px; }
  .hero-actions { gap: 20px; margin-top: 26px; }
  .course-meta { font-size: 11px; line-height: 2; }
  .course-meta span { margin: 0 6px; }
  .overview-nav { flex-direction: column; gap: 8px; padding-block: 14px; margin-bottom: 32px; }
  .overview-nav-links { gap: 6px 22px; }
  .overview-nav-links a { padding-block: 8px; }
  .prose { font-size: 15px; }
  .prose h2 { font-size: 22px; margin-top: 48px; padding-top: 23px; }
  .prose h3 { font-size: 18px; }
  .chapter-toc { margin-bottom: 32px; }
  .code-block figcaption { padding: 9px 12px; flex-wrap: wrap; gap: 6px 10px; }
  .code-block figcaption .file-link { flex: 1 1 100%; font-size: 11px; }
  .terminal-label { white-space: normal !important; max-width: calc(100% - 38px); }
  .copy { min-height: 32px; }
  .copy > span { display: none; }
  pre { font-size: 12px; padding: 17px 16px; }
  .code-line.highlighted { box-shadow: -16px 0 var(--highlight), 16px 0 var(--highlight); }
  .code-line.highlighted::before { left: -16px; }
  .preview-columns { grid-template-columns: 1fr; }
  .preview-columns > div { padding: 20px; }
  .preview-columns > div + div { border-left: 0; border-top: 1px solid var(--line); }
  .preview-heading { padding: 14px 18px; flex-wrap: wrap; }
  .preview-columns pre { font-size: 12px; }
  .project-results { grid-template-columns: 1fr; gap: 20px; }
  .project-results b { margin-bottom: 3px; }
  .flow { flex-direction: column; }
  .flow > i { transform: rotate(90deg); }
  .request-trace > li { grid-template-columns: 23px 1fr; gap: 10px; }
  .checkpoint { padding: 17px 18px; }
  .reading-dock { top: 105px; gap: 10px; padding-block: 10px; }
  .contents-toggle, .page-contents-toggle { padding: 9px 7px; gap: 6px; font-size: 12px; }
  .dock-current { padding-left: 12px; }
  .dock-current > strong { font-size: 11px; }
  .dock-next { font-size: 12px; padding: 7px 4px; gap: 6px; }
  .dock-next .icon { width: 15px; height: 15px; }
  .contents-dialog, .page-dialog { max-height: calc(100dvh - 32px); }
  .page-dialog .page-links { padding: 12px 20px 20px; }
  .contents-heading { padding: 20px; }
  .contents-heading h2 { font-size: 20px; }
  .contents-dialog .chapter-list { padding: 10px; }
  .contents-dialog .chapter-list > a { font-size: 13px; gap: 9px; }
  .contents-footer { padding: 20px; gap: 16px; }
  .chapter-list > a { gap: 14px; }
  .chapter-list strong { font-size: 15px; }
  .chapter-list small { font-size: 12px; }
  .pagination { gap: 20px; margin-top: 50px; }
  .pagination a { font-size: 12px; }
  .doc-footer { flex-direction: column; align-items: flex-start; gap: 10px; font-size: 11px; }
}
@media (max-width: 380px) {
  h1, .overview-article h1 { font-size: 28px; }
}
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  * { transition: none !important; }
}