:root {
  --ink: #101a31;
  --muted: #4d5e7b;
  --blue: #1769d2;
  --blue-soft: #eaf2ff;
  --security: #9b241b;
  --security-soft: #fff0ed;
  --paper: #ffffff;
  --page: #edf2f8;
  --line: #cbd6e6;
  --code: #0e1728;
  --shadow: 0 18px 44px rgba(25, 42, 70, .12);
  --content: 1080px;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: 82px; }
body { margin: 0; color: var(--ink); background: var(--page); font: 16px/1.58 Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif; }
a { color: #0757bb; text-underline-offset: .18em; }
button, select { font: inherit; }
button, a, select, summary { -webkit-tap-highlight-color: transparent; }
:focus-visible { outline: 3px solid #69c7f2; outline-offset: 3px; }
.sr-only { position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px; overflow: hidden; clip: rect(0, 0, 0, 0); white-space: nowrap; border: 0; }
.skip-link { position: fixed; z-index: 100; left: 16px; top: 12px; padding: 10px 14px; background: var(--ink); color: #fff; transform: translateY(-160%); }
.skip-link:focus { transform: translateY(0); }

.toolbar { position: sticky; top: 0; z-index: 30; display: flex; align-items: center; justify-content: space-between; gap: 20px; min-height: 68px; padding: 10px max(16px, calc((100vw - 1200px) / 2)); background: rgba(255,255,255,.97); border-bottom: 1px solid var(--line); backdrop-filter: blur(10px); }
.breadcrumb, .toolbar-actions { display: flex; align-items: center; gap: 10px; }
.breadcrumb { min-width: 0; font-size: .84rem; font-weight: 760; }
.breadcrumb a, .breadcrumb span { white-space: nowrap; }
.toolbar-actions select { max-width: 270px; padding: 10px 36px 10px 12px; border: 1px solid #aebbd0; border-radius: 8px; color: var(--ink); background: #fff; }
.button { display: inline-flex; align-items: center; justify-content: center; min-height: 42px; padding: 9px 15px; border: 1px solid #9eacc2; border-radius: 8px; background: #fff; color: var(--ink); font-weight: 760; text-decoration: none; cursor: pointer; }
.button-primary { border-color: var(--blue); background: var(--blue); color: #fff; }
.button.is-complete { border-color: #24724b; background: #e8f6ee; color: #175d3a; }

main { max-width: 1160px; margin: 32px auto; }
.toc-page, .lesson { background: var(--paper); box-shadow: var(--shadow); }
.toc-page { min-height: calc(100vh - 132px); padding: 70px 72px; }
.document-mark, .eyebrow, .mini-kicker { margin: 0 0 12px; color: var(--blue); font-size: .78rem; font-weight: 850; letter-spacing: .13em; text-transform: uppercase; }
.toc-page h1 { max-width: 900px; margin: 0; font-size: clamp(2.4rem, 6vw, 5rem); line-height: .99; letter-spacing: -.045em; }
.toc-intro { max-width: 860px; margin: 24px 0; color: var(--muted); font-size: 1.18rem; }
.safety-boundary { display: grid; gap: 5px; margin: 28px 0 24px; padding: 18px 20px; border: 2px solid var(--security); border-left-width: 8px; background: var(--security-soft); color: #661710; }
.safety-boundary strong { font-size: 1.05rem; text-transform: uppercase; letter-spacing: .045em; }
.course-status { display: flex; flex-wrap: wrap; gap: 9px 24px; margin: 22px 0; padding: 14px 18px; border: 1px solid var(--line); background: #f8faff; }
.days-overview { display: grid; gap: 14px; margin: 28px 0 38px; }
.day-overview { border: 1px solid var(--line); border-radius: 10px; overflow: hidden; }
.day-overview summary { display: grid; grid-template-columns: 90px 1fr; gap: 18px; align-items: center; padding: 18px 20px; cursor: pointer; background: #f8faff; }
.day-overview summary::marker { color: var(--blue); }
.day-overview summary strong, .day-overview summary small { display: block; }
.day-overview summary small { color: var(--muted); }
.day-number { color: var(--blue); font-weight: 850; text-transform: uppercase; }
.day-outcome { margin: 0; padding: 18px 22px 0; }
.overview-periods { display: grid; grid-template-columns: 1fr 1fr; gap: 18px; padding: 18px 22px 24px; }
.overview-period h3 { margin: 0 0 8px; font-size: .84rem; color: var(--muted); text-transform: uppercase; letter-spacing: .08em; }
.overview-period ol { margin: 0; padding: 0; list-style: none; border-top: 1px solid var(--line); }
.overview-period li a { display: grid; grid-template-columns: 72px 1fr; gap: 3px 12px; padding: 11px 2px; border-bottom: 1px solid var(--line); text-decoration: none; }
.overview-period li a span { grid-row: 1 / 3; color: var(--blue); font: 750 .82rem ui-monospace, monospace; }
.overview-period li a small { color: var(--muted); }
.overview-period li.is-optional { background: #f5f8fc; }
.course-facts { padding-top: 20px; border-top: 3px solid var(--ink); }
.course-facts h2 { font-size: 2rem; }
.facts-grid { display: grid; grid-template-columns: repeat(2, 1fr); gap: 12px; }
.facts-grid > div { padding: 16px; border: 1px solid var(--line); }
.facts-grid h3 { margin: 0 0 7px; font-size: .78rem; text-transform: uppercase; letter-spacing: .08em; }
.facts-grid p, .facts-grid ul { margin: 0; }

.course-document { display: grid; gap: 28px; margin-top: 28px; }
.day-heading { padding: 36px 54px; background: var(--ink); color: #fff; }
.day-heading p { max-width: 760px; margin-bottom: 0; color: #d4dced; }
.day-heading h2 { margin: 0; font-size: 2.3rem; }
.lesson { padding: 62px 70px; scroll-margin-top: 82px; }
.lesson-heading { padding-bottom: 25px; border-bottom: 1px solid var(--line); }
.lesson-meta { display: flex; flex-wrap: wrap; gap: 8px; }
.lesson-meta span { padding: 3px 9px; border-radius: 999px; background: var(--blue-soft); color: #0757bb; font-size: .78rem; font-weight: 760; }
.lesson-meta span:first-child { background: var(--security-soft); color: var(--security); }
.lesson h2 { margin: 13px 0 14px; font-size: clamp(2rem, 4vw, 3.2rem); line-height: 1.06; }
.lesson h2 > span { color: var(--blue); font: 800 .52em ui-monospace, monospace; letter-spacing: .03em; }
.safety-inline { margin: 20px 0; padding: 13px 16px; border-left: 5px solid var(--security); background: var(--security-soft); color: #661710; font-weight: 700; }
.security-grid, .practice-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 18px; margin: 24px 0; }
.security-grid > section, .practice-grid > section, .secure-design, .repository-card, .incident-template { padding: 20px; border: 1px solid var(--line); background: #fbfcfe; }
.security-grid h3, .practice-grid h3, .secure-design h3, .repository-card h3, .incident-template h3, .references h3 { margin-top: 0; }
.trust-boundary { border-top: 5px solid var(--blue) !important; }
.vulnerable-pattern { border-top: 5px solid var(--security) !important; }
.pattern-frame { position: relative; margin-top: 14px; padding: 19px; border-radius: 8px; background: var(--code); color: #e7edf8; font: .9rem/1.55 ui-monospace, SFMono-Regular, Consolas, monospace; }
.pattern-frame::before { content: "DESCRIPTIVE HANDOUT · NOT EXECUTABLE"; display: block; margin-bottom: 10px; color: #ffb8ae; font-size: .7rem; font-weight: 800; letter-spacing: .08em; }
.patch-objective { margin: 22px 0; padding: 20px; border-left: 5px solid var(--blue); background: var(--blue-soft); }
.secure-design { border-top: 5px solid #24724b; background: #f0faf4; }
.practice-grid ul { margin-bottom: 0; }
.regression-list { display: grid; gap: 8px; padding-left: 20px; }
.incident-template dl { display: grid; grid-template-columns: repeat(2, 1fr); gap: 10px; }
.incident-template dl div { min-height: 76px; padding: 10px; border: 1px dashed #aebbd0; }
.incident-template dt { font-size: .75rem; font-weight: 800; text-transform: uppercase; }
.incident-template dd { margin: 7px 0 0; color: var(--muted); }
.repository-card { margin: 24px 0; border-top: 5px solid var(--ink); }
.repository-card-heading { display: flex; justify-content: space-between; gap: 18px; }
.repository-meta { display: grid; grid-template-columns: 1fr 1fr; gap: 10px; }
.repository-meta div { padding: 10px; background: #eef3fa; }
.repository-meta dt { font-size: .72rem; font-weight: 800; text-transform: uppercase; }
.repository-meta dd { margin: 4px 0 0; }
.track-links { display: grid; grid-template-columns: repeat(3, 1fr); gap: 10px; margin: 15px 0; }
.track-links a { padding: 12px; border: 1px solid #9eacc2; border-radius: 7px; text-decoration: none; font-weight: 760; }
.track-links span { display: block; color: var(--blue); font-size: .72rem; }
.command-row { display: grid; grid-template-columns: 150px 1fr auto; align-items: center; gap: 10px; padding: 9px 0; border-top: 1px solid var(--line); }
.command-row code { overflow-wrap: anywhere; }
.copy-button { padding: 5px 8px; border: 1px solid #9eacc2; background: #fff; cursor: pointer; }
.hints, .extra-mile { margin: 14px 0; padding: 14px 17px; border: 1px solid var(--line); }
.hints summary, .extra-mile summary { cursor: pointer; font-weight: 800; }
.completion { margin: 20px 0; padding: 16px; border: 1px solid #24724b; background: #f0faf4; }
.lesson-actions { display: flex; flex-wrap: wrap; gap: 10px; margin: 20px 0; }
.references { margin-top: 30px; padding-top: 18px; border-top: 1px solid var(--line); }
.lesson-navigation { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; margin-top: 32px; }
.lesson-navigation a { padding: 14px; border: 1px solid var(--line); text-decoration: none; }
.lesson-navigation a span, .lesson-navigation a strong { display: block; }
.lesson-navigation a:last-child { text-align: right; }
.course-footer { display: flex; justify-content: space-between; gap: 18px; max-width: 1160px; margin: 28px auto; padding: 20px; border-top: 1px solid var(--line); font-size: .82rem; }

.quiz-dialog { width: min(760px, calc(100vw - 30px)); max-height: min(820px, calc(100vh - 30px)); padding: 0; border: 1px solid #8fa2bf; border-radius: 12px; color: var(--ink); background: #fff; box-shadow: 0 28px 90px rgba(0,0,0,.28); }
.quiz-dialog::backdrop { background: rgba(5, 11, 22, .72); backdrop-filter: blur(3px); }
.quiz-header { display: flex; justify-content: space-between; gap: 18px; padding: 18px 22px; border-bottom: 1px solid var(--line); }
.quiz-header p, .quiz-header h2 { margin: 0; }
.quiz-header p { color: var(--blue); font-size: .72rem; font-weight: 850; letter-spacing: .1em; }
.quiz-close { width: 40px; height: 40px; border: 1px solid #9eacc2; background: #fff; cursor: pointer; }
.quiz-body { padding: 22px; }
.quiz-review-setting { display: flex; gap: 9px; margin: 18px 0; }
.quiz-actions { display: flex; flex-wrap: wrap; gap: 9px; margin-top: 20px; }
.quiz-question { padding: 0; border: 0; }
.quiz-question legend { font-size: 1.25rem; font-weight: 800; }
.quiz-options { display: grid; gap: 9px; }
.quiz-options label { display: flex; gap: 10px; padding: 12px; border: 1px solid var(--line); }
.quiz-feedback { margin-top: 17px; padding: 15px; border-left: 5px solid var(--blue); background: var(--blue-soft); }
.quiz-feedback.is-correct { border-left-color: #24724b; background: #f0faf4; }
.quiz-review-list { display: grid; gap: 12px; }
.quiz-review-card { padding: 14px; border: 1px solid var(--line); }

@media (max-width: 820px) {
  .toolbar { align-items: flex-start; }
  .breadcrumb { display: none; }
  .toolbar-actions { width: 100%; flex-wrap: wrap; }
  .toolbar-actions select { flex: 1 1 160px; }
  main { margin: 0; }
  .toc-page, .lesson { padding: 38px 22px; box-shadow: none; }
  .overview-periods, .facts-grid, .security-grid, .practice-grid, .repository-meta, .track-links, .lesson-navigation { grid-template-columns: 1fr; }
  .incident-template dl { grid-template-columns: 1fr; }
  .command-row { grid-template-columns: 1fr; }
  .course-footer { flex-direction: column; margin: 0; }
}

@media print {
  @page { size: A4; margin: 15mm 14mm 16mm; }
  :root { --ink: #000; --muted: #333; --line: #aaa; }
  body { background: #fff; font-size: 10.2pt; }
  .screen-only, .quiz-dialog { display: none !important; }
  main, .course-footer { width: auto; max-width: none; margin: 0; }
  .toc-page, .lesson { min-height: auto; padding: 0; box-shadow: none; }
  .toc-page { break-after: page; }
  .day-heading { padding: 10mm 0; background: #fff; color: #000; break-before: page; }
  .day-heading p { color: #333; }
  .lesson { break-before: page; }
  .lesson h2 { font-size: 23pt; }
  .security-grid, .practice-grid, .facts-grid { gap: 5mm; }
  .repository-card, .incident-template, .security-grid > section, .practice-grid > section, .secure-design { break-inside: avoid; background: #fff; }
  details > * { display: block !important; }
  a { color: #000; text-decoration: none; }
  a[href^="http"]::after { content: " (" attr(href) ")"; font-size: 7.5pt; overflow-wrap: anywhere; }
  .course-footer { margin-top: 10mm; padding: 4mm 0; }
}