* { box-sizing: border-box; margin: 0; padding: 0; }
  html, body { font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", Helvetica, Arial, sans-serif; color: #222; background: #f4f6f8; line-height: 1.5; height: 100%; overflow: hidden; }
  body { padding-bottom: 64px; }
  section.slide {
    display: none;
    width: 100%;
    height: calc(100vh - 64px);
    height: calc(100dvh - 64px);
    padding: 5vh 6vw;
    flex-direction: column;
    overflow-y: auto;
  }
  section.slide.active { display: flex; }
  section.slide > .container { margin: auto 0; width: 100%; }
  section.slide.title-slide { background: linear-gradient(135deg, #1e3c72 0%, #2a5298 100%); color: #fff; text-align: center; align-items: center; }
  section.slide.title-slide > .container { margin: auto; }
  section.slide h1 { font-size: clamp(28px, 5vw, 56px); margin-bottom: 0.4em; }
  section.slide h2 { font-size: clamp(22px, 3.4vw, 36px); margin-bottom: 0.9em; color: #1e3c72; }
  section.slide.title-slide h2 { color: #cfe6ff; font-weight: 400; }
  section.slide p { font-size: clamp(15px, 1.8vw, 18px); margin-bottom: 0.7em; }
  section.slide ul { padding-left: 1.4em; margin-bottom: 0.7em; }
  section.slide li { font-size: clamp(15px, 1.8vw, 18px); margin-bottom: 0.4em; }
  .container { width: 100%; max-width: 1200px; margin: 0 auto; }
  .two-col { display: grid; grid-template-columns: 1fr 1fr; gap: 4vw; align-items: start; }
  @media (max-width: 768px) { .two-col { grid-template-columns: 1fr; gap: 2em; } }
  .panel { background: #e7f0fa; padding: clamp(18px, 2.4vw, 28px); border-radius: 10px; }
  .panel.white { background: #fff; box-shadow: 0 1px 4px rgba(0,0,0,0.08); }
  .panel h3 { color: #1e3c72; margin-bottom: 0.5em; font-size: clamp(16px, 2vw, 20px); }
  .ask-box { background: #fff; padding: clamp(14px, 2vw, 22px); border-left: 6px solid #2a5298; border-radius: 4px; margin: 0.6em 0; }
  .tip-box { background: #fffbe6; padding: clamp(12px, 1.6vw, 18px); border-left: 4px solid #f1c40f; border-radius: 4px; margin: 0.6em 0; font-size: clamp(13px, 1.6vw, 16px); }
  .figure-cap { font-size: 13px; color: #555; text-align: center; margin-top: 8px; }
  .role-grid { display: grid; grid-template-columns: repeat(2, 1fr); gap: 16px; }
  @media (max-width: 600px) { .role-grid { grid-template-columns: 1fr; } }
  .role-card { background: #fff; border-radius: 10px; padding: 18px; box-shadow: 0 1px 4px rgba(0,0,0,0.08); }
  .role-card .badge { display: inline-block; background: #1e3c72; color: #fff; font-size: 13px; padding: 3px 10px; border-radius: 12px; margin-bottom: 8px; }
  .role-card .badge.sys { background: #c0392b; }
  .role-card .badge.pres { background: #16a085; }
  .role-card .badge.vis { background: #7f8c8d; }
  .start-cta { display: flex; gap: 12px; flex-wrap: wrap; margin-top: 1em; }
  .start-cta a { display: inline-block; padding: 10px 18px; border-radius: 6px; text-decoration: none; font-weight: 600; }
  .start-cta a.primary { background: #1e3c72; color: white; }
  .start-cta a.secondary { background: #f1f3f5; color: #1e3c72; border: 1px solid #d0d7de; }
  .start-cta a:hover { opacity: 0.9; }

  /* --- Mock UI building blocks (deliberately small + decorative, not interactive) --- */
  .mock {
    background: #fff;
    border: 1px solid #e3e7eb;
    border-radius: 8px;
    padding: 14px;
    box-shadow: 0 2px 8px rgba(0,0,0,0.06);
    font-size: 13px;
    color: #333;
  }
  .mock .mock-bar {
    background: linear-gradient(135deg, #1e3c72 0%, #2a5298 100%);
    color: white;
    padding: 8px 12px;
    border-radius: 6px 6px 0 0;
    margin: -14px -14px 12px;
    font-weight: 600;
    display: flex;
    justify-content: space-between;
    align-items: center;
  }
  .mock .mock-btn {
    display: inline-block;
    background: #1e3c72;
    color: white;
    padding: 5px 12px;
    border-radius: 4px;
    font-size: 12px;
    margin-right: 4px;
  }
  .mock .mock-btn.danger { background: #dc3545; }
  .mock .mock-btn.success { background: #28a745; }
  .mock .mock-btn.muted { background: #6c757d; }
  .mock .mock-input,
  .mock .mock-select {
    border: 1px solid #ccc;
    background: #fafafa;
    padding: 5px 8px;
    border-radius: 4px;
    font-size: 12px;
    margin: 2px 0;
    display: inline-block;
    min-width: 130px;
  }
  .mock .mock-textarea {
    border: 1px solid #ccc;
    background: #fafafa;
    padding: 6px 8px;
    border-radius: 4px;
    font-size: 12px;
    width: 100%;
    min-height: 50px;
    margin-top: 4px;
    color: #888;
    font-family: monospace;
  }
  .mock .mock-row { display: flex; gap: 8px; margin: 6px 0; align-items: center; flex-wrap: wrap; }
  .mock .mock-tile {
    border-radius: 8px;
    overflow: hidden;
    box-shadow: 0 2px 6px rgba(0,0,0,0.1);
  }
  .mock .mock-tile .head { padding: 10px 12px; color: white; font-weight: 700; font-size: 14px; }
  .mock .mock-tile .body { padding: 10px 12px; background: white; font-size: 11px; color: #555; line-height: 1.4; }
  .mock .mock-tile .tags { margin-top: 6px; }
  .mock .mock-tile .tags span { display: inline-block; background: #f0f0f0; color: #555; padding: 1px 6px; border-radius: 8px; font-size: 10px; margin-right: 3px; }
  .mock-tiles-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 8px; margin-top: 8px; }
  .mock-table { width: 100%; border-collapse: collapse; font-size: 12px; margin-top: 6px; }
  .mock-table th, .mock-table td { text-align: left; padding: 6px 8px; border-bottom: 1px solid #eee; }
  .mock-table th { background: #f7f9fc; font-weight: 600; color: #1e3c72; }
  .mock-arrow { font-size: 22px; color: #1e3c72; text-align: center; line-height: 1; }
  .mock-chip { display: inline-block; background: #e7f0fa; color: #1e3c72; padding: 2px 8px; border-radius: 10px; font-size: 11px; margin: 2px; }
  .mock-phone {
    width: 180px;
    border: 6px solid #222;
    border-radius: 18px;
    background: white;
    padding: 6px;
    margin: 0 auto;
    box-shadow: 0 4px 12px rgba(0,0,0,0.15);
  }
  .mock-phone .screen {
    background: linear-gradient(135deg, #1e3c72 0%, #0f9b8e 100%);
    color: white;
    border-radius: 10px;
    padding: 10px;
    text-align: center;
    font-size: 12px;
    height: 240px;
    display: flex;
    flex-direction: column;
    justify-content: space-between;
  }
  .mock-phone .screen .play-btn {
    background: rgba(255,255,255,0.2);
    border: 2px solid white;
    border-radius: 50%;
    width: 60px;
    height: 60px;
    line-height: 56px;
    font-size: 28px;
    margin: 30px auto;
  }

  /* Language toggle: show one at a time */
  body.lang-en .zh { display: none; }
  body.lang-zh .en { display: none; }

  /* Bottom navigation bar */
  .navbar {
    position: fixed; left: 0; right: 0; bottom: 0; height: 64px;
    background: #ffffff; border-top: 1px solid #d0d7de;
    display: flex; align-items: center; justify-content: space-between;
    padding: 0 16px; z-index: 100;
    box-shadow: 0 -2px 8px rgba(0,0,0,0.06);
  }
  .navbar button {
    background: #1e3c72; color: #fff; border: none;
    padding: 10px 18px; font-size: 15px; border-radius: 6px;
    cursor: pointer; min-width: 100px;
    transition: background 0.15s;
  }
  .navbar button:hover:not(:disabled) { background: #163058; }
  .navbar button:disabled { background: #b8c2cd; cursor: not-allowed; }
  .navbar .counter { font-size: 14px; color: #444; font-weight: 600; }
  .navbar .counter .total { color: #888; font-weight: 400; }
  .navbar .lang-btn {
    background: #fff; color: #1e3c72; border: 1px solid #1e3c72;
    min-width: 70px; padding: 8px 14px; font-weight: 600;
  }
  .navbar .lang-btn:hover { background: #eaf2fa; }
  .navbar .home-link {
    color: #1e3c72; text-decoration: none; font-weight: 600; font-size: 14px;
    padding: 6px 10px; border-radius: 4px;
  }
  .navbar .home-link:hover { background: #eaf2fa; }
  @media (max-width: 480px) {
    .navbar button { padding: 10px 10px; font-size: 13px; min-width: 60px; }
    .navbar .lang-btn { min-width: 56px; padding: 8px 10px; }
    .navbar .home-link { font-size: 12px; padding: 6px 6px; }
  }