:root {
  --bg: #ffffff;
  --text: #202124;
  --muted: #5f6368;
  --line: #d9dce1;
  --soft: #f5f6f7;
  --accent: #1f5fbf;
  --accent-soft: #eaf1ff;
  --warn: #fff8e6;
  --note: #eef7ee;
  --pitfall: #fff0f0;
  --max: 920px;
}
* { box-sizing: border-box; }
body { margin: 0; font-family: Arial, Helvetica, sans-serif; font-size: 16px; line-height: 1.55; color: var(--text); background: var(--bg); }
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }
.site-header { border-bottom: 1px solid var(--line); background: var(--soft); }
.header-inner { max-width: var(--max); margin: 0 auto; padding: 14px 18px; display: flex; align-items: center; justify-content: space-between; gap: 16px; }
.logo { font-weight: 700; font-size: 20px; color: var(--text); }
.top-nav { display: flex; flex-wrap: wrap; gap: 14px; font-size: 14px; }
.top-nav a.active { font-weight: 700; color: var(--text); }
.main { max-width: var(--max); margin: 0 auto; padding: 24px 18px 48px; }
.hero { border-bottom: 1px solid var(--line); padding-bottom: 22px; margin-bottom: 24px; }
.hero h1 { margin: 0 0 8px; font-size: 34px; line-height: 1.15; }
.lede { font-size: 18px; color: var(--muted); max-width: 700px; }
.quick-links { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 16px; }
.button { display: inline-block; border: 1px solid var(--accent); background: var(--accent); color: white; padding: 8px 12px; border-radius: 4px; font-weight: 700; }
.button.secondary { background: white; color: var(--accent); }
.grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 16px; }
.card { border: 1px solid var(--line); border-radius: 6px; padding: 16px; background: white; }
.card h2, .card h3 { margin-top: 0; }
.card p { color: var(--muted); }
.placeholder-image { height: 120px; border: 1px dashed #aeb4bd; background: #f1f3f4; display: flex; align-items: center; justify-content: center; color: var(--muted); margin-bottom: 12px; font-size: 14px; text-align: center; padding: 10px; }
.breadcrumbs { font-size: 14px; color: var(--muted); margin-bottom: 14px; }
.layout { display: grid; grid-template-columns: 220px minmax(0, 1fr); gap: 24px; }
.sidebar { border: 1px solid var(--line); background: var(--soft); padding: 12px; align-self: start; position: sticky; top: 12px; }
.sidebar h2 { font-size: 16px; margin: 0 0 8px; }
.sidebar ul { list-style: none; padding: 0; margin: 0; }
.sidebar li { margin: 6px 0; }
.sidebar a.current { font-weight: 700; color: var(--text); }
.lesson-title { border-bottom: 1px solid var(--line); padding-bottom: 14px; margin-bottom: 18px; }
.lesson-title h1 { margin: 0 0 8px; font-size: 30px; }
.meta { color: var(--muted); font-size: 14px; }
.objectives, .summary-box { border: 1px solid var(--line); background: var(--soft); padding: 14px 16px; border-radius: 6px; margin: 16px 0; }
.step { border-top: 1px solid var(--line); padding-top: 20px; margin-top: 20px; }
.step h2 { font-size: 22px; margin-bottom: 8px; }
.callout { border-left: 4px solid var(--accent); background: var(--accent-soft); padding: 10px 12px; margin: 12px 0; }
.callout.note { border-color: #3c7c3c; background: var(--note); }
.callout.warn { border-color: #b88300; background: var(--warn); }
.callout.pitfall { border-color: #b33a3a; background: var(--pitfall); }
.callout strong { display: block; margin-bottom: 4px; }
.lesson-nav { display: flex; justify-content: space-between; gap: 16px; border-top: 1px solid var(--line); margin-top: 30px; padding-top: 18px; }
.lesson-nav div:last-child { text-align: right; margin-left: auto; }
.footer { border-top: 1px solid var(--line); color: var(--muted); font-size: 14px; padding: 18px; text-align: center; }
.footer p { margin: 4px 0; }
.checklist { list-style: none; padding-left: 0; }
.checklist li { margin: 8px 0; }
@media (max-width: 760px) { .header-inner { align-items: flex-start; flex-direction: column; } .grid { grid-template-columns: 1fr; } .layout { grid-template-columns: 1fr; } .sidebar { position: static; } .hero h1 { font-size: 28px; } }
@media print { .site-header, .sidebar, .lesson-nav, .footer, .quick-links { display: none; } .main { max-width: none; padding: 0; } a { color: black; text-decoration: none; } }