/* Lesson-specific CSS extracted from javascript/01-history.html */

    /* ===== 리셋 & 기본 ===== */
    *, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
    :root{
      --bg: var(--page);
      --card: var(--panel);
      --primary: var(--primary-ui);
      --primary-light: var(--primary-ui-pale);
      --primary-dark: var(--primary-ui-hover);
      --accent: #f72585;
      --text: var(--ink);
      --sub: var(--ink-sub);
      --muted: var(--ink-muted);
      --border: var(--line);
      --code-bg: #1e1e2e;
      --radius: 12px;
      --orange: #f97316;
      --blue: #3b82f6;
    }
    body {
      font-family: 'Segoe UI', 'Noto Sans KR', sans-serif;
      background: var(--bg);
      color: var(--text);
      line-height: 1.6;
    }

    /* ===== 사이드바 네비 ===== */
    .sidebar {
      position: fixed;
      left: 0; top: 0; bottom: 0;
      width: 220px;
      background: var(--card);
      border-right: 1px solid var(--border);
      padding: 24px 0;
      overflow-y: auto;
      z-index: 100;
      transition: transform 0.3s ease;
    }
    .sidebar.collapsed { transform: translateX(-220px); }
    .sidebar.open { transform: translateX(0); }

    .sidebar-header {
      display: flex;
      align-items: center;
      justify-content: space-between;
      padding: 0 20px 16px;
      border-bottom: 1px solid var(--border);
      margin-bottom: 12px;
    }
    .sidebar-title {
      font-size: 13px;
      font-weight: 700;
      color: var(--primary-dark);
      letter-spacing: 0.05em;
    }
    .sidebar-toggle {
      display: none;
      background: none; border: none;
      cursor: pointer; font-size: 18px;
      color: var(--sub); padding: 2px;
      line-height: 1;
    }

    .nav-home {
      display: flex; align-items: center; gap: 8px;
      padding: 8px 20px 12px;
      font-size: 12px; font-weight: 600;
      color: var(--primary); text-decoration: none;
      border-bottom: 1px solid var(--border);
      margin-bottom: 8px;
      transition: all 0.15s;
    }
    .nav-home:hover { background: var(--primary-light); }
    .nav-home-icon { font-size: 14px; }

    .nav-item {
      display: block;
      padding: 8px 20px;
      font-size: 13px;
      color: var(--sub);
      text-decoration: none;
      transition: all 0.15s;
      border-left: 3px solid transparent;
    }
    .nav-item:hover { color: var(--primary); background: var(--primary-light); }
    .nav-item.active { color: var(--primary); border-left-color: var(--primary); background: var(--primary-light); font-weight: 600; }
    .nav-num { font-family: monospace; font-size: 11px; color: var(--muted); margin-right: 6px; }

    /* 모바일 햄버거 버튼 */
    .menu-btn {
      display: none;
      position: fixed;
      top: 12px; left: 12px;
      z-index: 200;
      background: var(--primary);
      color: #fff;
      border: none; border-radius: 8px;
      width: 40px; height: 40px;
      font-size: 18px; cursor: pointer;
      align-items: center; justify-content: center;
      box-shadow: 0 2px 8px rgba(0,0,0,0.15);
      transition: all 0.15s;
    }
    .menu-btn:hover { opacity: 0.85; }

    .sidebar-overlay {
      display: none;
      position: fixed; inset: 0;
      background: rgba(0,0,0,0.3);
      z-index: 99;
      backdrop-filter: blur(2px);
    }
    .sidebar-overlay.show { display: block; }

    /* ===== 메인 콘텐츠 ===== */
    .main { margin-left: 220px; padding: 40px 40px 100px; max-width: 960px; transition: margin 0.3s; }

    /* ===== 반응형 ===== */
    @media (max-width: 768px) {
      .sidebar { transform: translateX(-220px); }
      .sidebar.open { transform: translateX(0); }
      .menu-btn { display: flex; }
      .sidebar-toggle { display: block; }
      .main { margin-left: 0; padding: 60px 16px 80px; }
    }

    /* ===== 히어로 ===== */
    .hero {
      text-align: center;
      padding: 60px 20px 48px;
      background: linear-gradient(135deg, #10b981 0%, #059669 100%);
      border-radius: var(--radius);
      color: #fff;
      margin-bottom: 48px;
    }
    .hero h1 { font-size: 36px; font-weight: 800; margin-bottom: 12px; letter-spacing: -1px; }
    .hero p { font-size: 16px; opacity: 0.9; }
    .hero-badges { display: flex; gap: 8px; justify-content: center; margin-top: 20px; flex-wrap: wrap; }
    .hero-badge {
      background: rgba(255,255,255,0.2);
      border: 1px solid rgba(255,255,255,0.3);
      color: #fff;
      font-size: 12px;
      padding: 4px 12px;
      border-radius: 20px;
      font-weight: 500;
    }

    /* ===== 섹션 ===== */
    .section { margin-bottom: 64px; scroll-margin-top: 24px; }
    .section-header { margin-bottom: 24px; }
    .section-num {
      font-size: 12px;
      font-weight: 700;
      color: var(--primary);
      letter-spacing: 0.1em;
      margin-bottom: 6px;
    }
    .section-title { font-size: 26px; font-weight: 800; color: var(--text); margin-bottom: 8px; letter-spacing: -0.5px; }
    .section-desc { font-size: 14px; color: var(--sub); line-height: 1.7; }

    /* ===== 카드 ===== */
    .card {
      background: var(--card);
      border: 1px solid var(--border);
      border-radius: var(--radius);
      overflow: hidden;
      margin-bottom: 20px;
    }
    .card-title {
      font-size: 13px;
      font-weight: 600;
      color: var(--sub);
      padding: 12px 16px;
      border-bottom: 1px solid var(--border);
      background: var(--bg);
      display: flex;
      align-items: center;
      gap: 8px;
    }
    .dot {
      width: 8px; height: 8px;
      border-radius: 50%;
    }
    .dot-green { background: var(--primary); }
    .dot-orange { background: var(--orange); }
    .dot-blue { background: var(--blue); }

    /* ===== 코드 블록 ===== */
    .code-block {
      background: var(--code-bg);
      padding: 20px;
      font-family: 'Fira Code', 'Courier New', monospace;
      font-size: 13px;
      color: #cdd6f4;
      line-height: 2;
      overflow-x: auto;
    }
    .code-block .cm   { color: #6c7086; }
    .code-block .sel  { color: #cba6f7; }
    .code-block .prop { color: #89b4fa; }
    .code-block .val  { color: #a6e3a1; }
    .code-block .str  { color: #f38ba8; }

    /* ===== 라이브 프리뷰 ===== */
    .preview {
      padding: 20px;
      background: #f1f5f9;
      min-height: 80px;
    }
    .preview-label {
      font-size: 11px;
      color: var(--muted);
      font-weight: 600;
      letter-spacing: 0.08em;
      margin-bottom: 12px;
    }

    /* 프리뷰 요소들 */
    .timeline-item {
      margin: 15px 0;
      padding: 15px;
      background: white;
      border-radius: 0px;
      border-left: 3px solid var(--primary);
    }
    .timeline-item strong {
      color: var(--primary);
      display: block;
      margin-bottom: 5px;
    }

    .browser-list {
      display: flex;
      gap: 12px;
      flex-wrap: wrap;
    }
    .browser-item {
      flex: 1;
      min-width: 120px;
      padding: 12px;
      background: white;
      border: 1px solid var(--border);
      border-radius: 0px;
      text-align: center;
    }
    .browser-item .name {
      font-size: 12px;
      font-weight: 600;
      color: var(--text);
      margin-bottom: 4px;
    }
    .browser-item .year {
      font-size: 11px;
      color: var(--primary);
      font-weight: 600;
    }

    /* ===== 테이블 ===== */
    table {
      width: 100%;
      border-collapse: collapse;
      margin: 20px 0;
      background: white;
    }
    table th {
      background: var(--primary);
      color: white;
      padding: 12px;
      text-align: left;
      font-weight: 600;
    }
    table td {
      padding: 12px;
      border-bottom: 1px solid var(--border);
    }
    table tr:hover {
      background: var(--primary-light);
    }

    /* ===== 팁 박스 ===== */
    .tip {
      border-left: 3px solid var(--primary);
      background: var(--primary-light);
      padding: 12px 16px;
      border-radius: 0 8px 8px 0;
      font-size: 13px;
      color: var(--primary-dark);
      margin-top: 16px;
      line-height: 1.7;
    }
    .tip.orange { border-color: var(--orange); background: #fed7aa; color: #9a3412; }
    .tip.blue { border-color: var(--blue); background: #dbeafe; color: #1e3a8a; }

    /* ===== 비교 ===== */
    .compare { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; margin: 20px 0; }
    .compare-card { background: var(--card); border: 1px solid var(--border); border-radius: var(--radius); overflow: hidden; }
    .compare-title { font-size: 12px; font-weight: 600; padding: 10px 14px; border-bottom: 1px solid var(--border); background: var(--bg); }

    /* ===== 컨트롤 ===== */
    .controls { padding: 16px 20px; border-top: 1px solid var(--border); background: var(--card); display: flex; flex-wrap: wrap; gap: 14px; align-items: center; }
    .ctrl-group { display: flex; align-items: center; gap: 10px; }
    .ctrl-label { font-size: 12px; color: var(--sub); font-weight: 500; min-width: 90px; }
    .tab-btns { display: flex; gap: 6px; flex-wrap: wrap; }
    .tab-btn {
      font-size: 12px; padding: 5px 12px; border-radius: 20px;
      border: 1px solid var(--border); background: var(--card);
      color: var(--sub); cursor: pointer; transition: all 0.15s; font-weight: 500;
    }
    .tab-btn.active { background: var(--primary); color: #fff; border-color: var(--primary); }

    /* ===== divider ===== */
    .divider { border: none; border-top: 1px solid var(--border); margin: 32px 0; }

    /* ===== 배지 ===== */
    .badge {
      display: inline-block; font-size: 11px; padding: 2px 8px;
      border-radius: 20px; font-weight: 600; margin-left: 6px;
    }
    .badge-green { background: var(--primary-light); color: var(--primary-dark); }

    /* ===== 리스트 ===== */
    ul { margin: 15px 0 15px 20px; padding: 0; }
    ul li { margin-bottom: 8px; color: var(--sub); line-height: 1.7; }