:root {
    --paper: #F1F4F8;
    --ink: #16213E;
    --ink-soft: #56618A;
    --line: #C9D2E3;
    --card-bg: #FFFFFF;
    --accent: #B23A2E;
    --accent-soft: #F3DEDB;
    --accent-ink: #7A2119;
    --success: #1F7A5C;
    --success-soft: #DCEFE7;
    --gold: #9C7A12;
    --gold-soft: #F3EAC9;
    --font-serif: 'Spectral', Georgia, 'Times New Roman', serif;
    --font-sans: 'IBM Plex Sans', -apple-system, 'Segoe UI', Roboto, sans-serif;
    --radius: 3px;
    box-sizing: border-box;
    padding-top: env(safe-area-inset-top, 0px);
    padding-bottom: env(safe-area-inset-bottom, 0px);
  }
  @media (prefers-color-scheme: dark) {
    :root:not([data-theme="light"]) {
      --paper: #11141D;
      --ink: #ECEFF6;
      --ink-soft: #9AA5C4;
      --line: #2B3350;
      --card-bg: #171B28;
      --accent: #E2685A;
      --accent-soft: #362023;
      --accent-ink: #F0A79C;
      --success: #4FBF95;
      --success-soft: #163229;
      --gold: #E0BB4B;
      --gold-soft: #332C14;
    }
  }
  :root[data-theme="dark"] {
    --paper: #11141D; --ink: #ECEFF6; --ink-soft: #9AA5C4; --line: #2B3350;
    --card-bg: #171B28; --accent: #E2685A; --accent-soft: #362023; --accent-ink: #F0A79C;
    --success: #4FBF95; --success-soft: #163229; --gold: #E0BB4B; --gold-soft: #332C14;
  }
  * { box-sizing: border-box; }
  html, body { height: 100%; }
  html { scroll-padding-top: env(safe-area-inset-top, 0px); }
  body {
    margin: 0; background: var(--paper); color: var(--ink);
    font-family: var(--font-sans); font-size: 15px; line-height: 1.55;
    -webkit-font-smoothing: antialiased;
  }
  h1, h2, h3 { font-family: var(--font-serif); font-weight: 600; margin: 0 0 .3em; letter-spacing: .1px; }
  a { color: inherit; }
  button { font-family: inherit; }
  .wrap { max-width: 980px; margin: 0 auto; padding: 0 20px; }
  .overflow-x { overflow-x: auto; }

  /* header */
  header.site {
    position: sticky; top: 0; z-index: 20; background: var(--paper);
    border-bottom: 1px solid var(--line); padding-top: env(safe-area-inset-top, 0px);
  }
  .site-bar { display: flex; align-items: center; justify-content: space-between; padding: 16px 20px; gap: 12px; }
  .brand { display: flex; align-items: baseline; gap: 10px; cursor: pointer; }
  .brand .mark { font-family: var(--font-serif); font-size: 1.5rem; font-weight: 700; }
  .brand .tagline { font-size: .78rem; color: var(--ink-soft); display: none; }
  @media (min-width: 640px) { .brand .tagline { display: inline; } }
  .session-chip { display: flex; align-items: center; gap: 10px; font-size: .88rem; }
  .role-pill { border: 1px solid var(--line); padding: 5px 10px; border-radius: var(--radius); color: var(--ink-soft); }
  .role-pill.is-admin { border-color: var(--accent); color: var(--accent-ink); background: var(--accent-soft); }
  .role-pill.is-student { border-color: var(--success); background: var(--success-soft); color: var(--success); }

  /* buttons */
  .btn {
    display: inline-flex; align-items: center; gap: 8px; border: 1px solid var(--ink);
    background: var(--ink); color: var(--paper); padding: 10px 16px; border-radius: var(--radius);
    font-size: .9rem; font-weight: 500; cursor: pointer; text-decoration: none; line-height: 1.2;
  }
  .btn:focus-visible, a:focus-visible, [tabindex]:focus-visible, input:focus-visible, textarea:focus-visible, select:focus-visible {
    outline: 2px solid var(--accent); outline-offset: 2px;
  }
  .btn.ghost { background: transparent; color: var(--ink); }
  .btn.small { padding: 6px 12px; font-size: .82rem; }
  .btn.danger { border-color: var(--accent); background: transparent; color: var(--accent); }
  .btn.accent { border-color: var(--accent); background: var(--accent); color: #fff; }
  .btn[disabled] { opacity: .5; cursor: not-allowed; }
  .btn-row { display: flex; gap: 10px; flex-wrap: wrap; }

  /* breadcrumb */
  .crumb { font-size: .85rem; color: var(--ink-soft); margin: 22px 0 6px; display: flex; gap: 6px; flex-wrap: wrap; }
  .crumb a { text-decoration: none; border-bottom: 1px solid transparent; }
  .crumb a:hover { border-bottom-color: var(--ink-soft); }

  .page-head { margin: 6px 0 28px; display: flex; justify-content: space-between; align-items: flex-end; gap: 16px; flex-wrap: wrap; }
  .page-head h1 { font-size: 1.7rem; }
  .page-head p { color: var(--ink-soft); margin: 0; max-width: 60ch; }

  /* ticket cards (exam list) */
  .ticket-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(250px, 1fr)); gap: 18px; margin-bottom: 32px; }
  .ticket {
    border: 1px solid var(--line); background: var(--card-bg); border-radius: var(--radius);
    padding: 20px 20px 0; position: relative; display: flex; flex-direction: column; text-decoration: none; color: inherit;
  }
  .ticket .code {
    display: inline-block; font-size: .72rem; border: 1px solid var(--accent); color: var(--accent-ink);
    background: var(--accent-soft); padding: 3px 8px; border-radius: var(--radius); align-self: flex-start; margin-bottom: 14px;
    font-family: var(--font-sans); font-weight: 600;
  }
  .ticket h3 { font-size: 1.25rem; margin-bottom: 6px; }
  .ticket .tagline { color: var(--ink-soft); font-size: .86rem; margin-bottom: 18px; min-height: 2.6em; }
  .ticket .stub {
    border-top: 1px dashed var(--line); margin-top: auto; padding: 12px 0; display: flex;
    justify-content: space-between; align-items: center; font-size: .85rem; font-weight: 500;
  }
  .ticket .stub .go { color: var(--accent-ink); }
  .ticket:hover .stub .go { text-decoration: underline; }

  .add-ticket {
    border: 1px dashed var(--line); border-radius: var(--radius); display: flex; align-items: center;
    justify-content: center; min-height: 150px; background: transparent; color: var(--ink-soft);
    cursor: pointer; font-size: .92rem; font-family: inherit;
  }
  .add-ticket:hover { border-color: var(--ink-soft); color: var(--ink); }

  /* ledger list (sections / tests) */
  .ledger { border-top: 1px solid var(--line); margin-bottom: 32px; }
  .ledger-row {
    display: flex; align-items: center; justify-content: space-between; gap: 16px;
    padding: 18px 4px; border-bottom: 1px solid var(--line); text-decoration: none; color: inherit;
  }
  .ledger-row .lr-main { min-width: 0; }
  .ledger-row h3 { font-size: 1.05rem; margin-bottom: 3px; }
  .ledger-row .meta { color: var(--ink-soft); font-size: .84rem; }
  .ledger-row .go-arrow { color: var(--ink-soft); font-size: 1.1rem; flex-shrink: 0; }
  .ledger-row:hover { background: var(--accent-soft); }
  .ledger-row:hover .go-arrow { color: var(--accent-ink); }

  .empty-box {
    border: 1px dashed var(--line); border-radius: var(--radius); padding: 32px 20px; text-align: center;
    color: var(--ink-soft); margin-bottom: 28px;
  }
  .empty-box .btn { margin-top: 14px; }

  /* modal */
  .modal-overlay {
    position: fixed; inset: 0; background: rgba(10, 14, 26, .55); display: flex; align-items: flex-start;
    justify-content: center; padding: 40px 16px; z-index: 100; overflow-y: auto;
  }
  .modal-box {
    background: var(--card-bg); border: 1px solid var(--line); border-radius: var(--radius);
    width: 100%; max-width: 460px; padding: 26px; margin-top: env(safe-area-inset-top, 0px);
  }
  .modal-box.wide { max-width: 640px; }
  .modal-head { display: flex; justify-content: space-between; align-items: flex-start; margin-bottom: 16px; gap: 10px; }
  .modal-head h2 { font-size: 1.25rem; margin: 0; }
  .modal-close { background: none; border: none; color: var(--ink-soft); font-size: 1.3rem; cursor: pointer; line-height: 1; padding: 4px; }

  .field { margin-bottom: 14px; }
  .field label { display: block; font-size: .82rem; color: var(--ink-soft); margin-bottom: 5px; }
  .field input[type=text], .field input[type=number], .field input[type=password], .field textarea, .field select {
    width: 100%; padding: 10px 11px; border: 1px solid var(--line); border-radius: var(--radius);
    background: var(--paper); color: var(--ink); font-family: inherit; font-size: .92rem;
  }
  .field textarea { resize: vertical; min-height: 64px; }
  .field-hint { font-size: .78rem; color: var(--ink-soft); margin-top: 4px; }
  .field-error { font-size: .8rem; color: var(--accent); margin-top: 4px; }

  .role-choice { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; margin-bottom: 18px; }
  .role-choice button {
    border: 1px solid var(--line); background: transparent; border-radius: var(--radius); padding: 16px 10px;
    cursor: pointer; font-family: inherit; color: var(--ink); text-align: center;
  }
  .role-choice button.active { border-color: var(--ink); background: var(--accent-soft); }
  .role-choice .rtitle { display: block; font-weight: 600; margin-bottom: 3px; }
  .role-choice .rsub { font-size: .78rem; color: var(--ink-soft); }

  /* admin panel */
  .admin-tabs { display: flex; gap: 8px; margin: 20px 0 22px; flex-wrap: wrap; }
  .admin-tabs button {
    border: 1px solid var(--line); background: transparent; padding: 8px 14px; border-radius: var(--radius);
    cursor: pointer; font-family: inherit; font-size: .86rem; color: var(--ink-soft);
  }
  .admin-tabs button.active { border-color: var(--ink); color: var(--ink); background: var(--card-bg); }
  .tree-exam { border: 1px solid var(--line); border-radius: var(--radius); margin-bottom: 16px; background: var(--card-bg); }
  .tree-exam > .tree-head { display: flex; justify-content: space-between; align-items: center; padding: 16px 18px; }
  .tree-exam .badge-code { font-size: .7rem; border: 1px solid var(--accent); color: var(--accent-ink); background: var(--accent-soft); padding: 2px 7px; border-radius: var(--radius); margin-right: 8px; }
  .tree-section { border-top: 1px solid var(--line); padding: 14px 18px; }
  .tree-section-head { display: flex; justify-content: space-between; align-items: center; gap: 10px; }
  .tree-test { display: flex; justify-content: space-between; align-items: center; padding: 10px 0 10px 16px; border-top: 1px dashed var(--line); gap: 10px; }
  .tree-test:first-of-type { border-top: none; margin-top: 8px; }
  .icon-btn { background: none; border: none; color: var(--ink-soft); cursor: pointer; padding: 4px 6px; font-size: .85rem; }
  .icon-btn:hover { color: var(--ink); }
  .icon-btn.danger:hover { color: var(--accent); }

  /* quiz */
  .quiz-topbar { display: flex; justify-content: space-between; align-items: center; margin: 18px 0; gap: 14px; flex-wrap: wrap; }
  .timer-pill {
    border: 1px solid var(--ink); border-radius: var(--radius); padding: 8px 14px; font-variant-numeric: tabular-nums;
    font-size: 1rem; font-weight: 600;
  }
  .timer-pill.low { border-color: var(--accent); color: var(--accent-ink); background: var(--accent-soft); }
  .progress-track { display: flex; flex-wrap: wrap; gap: 6px; margin-bottom: 26px; }
  .progress-dot {
    width: 30px; height: 30px; border-radius: var(--radius); border: 1px solid var(--line); display: flex;
    align-items: center; justify-content: center; font-size: .78rem; color: var(--ink-soft); background: transparent; cursor: pointer;
  }
  .progress-dot.answered { background: var(--ink); border-color: var(--ink); color: var(--paper); }
  .progress-dot.current { border-color: var(--accent); border-width: 2px; color: var(--accent-ink); }

  .q-card { border: 1px solid var(--line); border-radius: var(--radius); background: var(--card-bg); padding: 26px; margin-bottom: 22px; }
  .q-number { font-size: .8rem; color: var(--ink-soft); margin-bottom: 8px; }
  .q-text { font-size: 1.08rem; margin-bottom: 20px; }
  .q-option {
    display: flex; align-items: flex-start; gap: 12px; border: 1px solid var(--line); border-radius: var(--radius);
    padding: 12px 14px; margin-bottom: 10px; cursor: pointer; background: transparent;
  }
  .q-option:hover { border-color: var(--ink-soft); }
  .q-option.selected { border-color: var(--ink); background: var(--accent-soft); }
  .q-option .bubble {
    width: 26px; height: 26px; border-radius: 50%; border: 1px solid var(--ink-soft); flex-shrink: 0;
    display: flex; align-items: center; justify-content: center; font-size: .82rem; font-weight: 600; color: var(--ink-soft);
  }
  .q-option.selected .bubble { background: var(--ink); border-color: var(--ink); color: var(--paper); }
  .q-option.correct { border-color: var(--success); background: var(--success-soft); }
  .q-option.correct .bubble { background: var(--success); border-color: var(--success); color: #fff; }
  .q-option.incorrect { border-color: var(--accent); background: var(--accent-soft); }
  .q-option.incorrect .bubble { background: var(--accent); border-color: var(--accent); color: #fff; }
  .q-explain { font-size: .86rem; color: var(--ink-soft); border-top: 1px dashed var(--line); margin-top: 14px; padding-top: 12px; }

  .quiz-nav { display: flex; justify-content: space-between; margin: 20px 0 60px; }

  .score-hero { border: 1px solid var(--line); border-radius: var(--radius); background: var(--card-bg); padding: 34px 26px; text-align: center; margin: 20px 0 30px; }
  .score-hero .big { font-family: var(--font-serif); font-size: 3rem; font-weight: 700; }
  .score-hero .sub { color: var(--ink-soft); margin-top: 6px; }

  table.attempts { width: 100%; border-collapse: collapse; font-size: .88rem; }
  table.attempts th, table.attempts td { text-align: left; padding: 8px 10px; border-bottom: 1px solid var(--line); }
  table.attempts th { color: var(--ink-soft); font-weight: 500; }

  footer.site { padding: 40px 20px 30px; text-align: center; color: var(--ink-soft); font-size: .82rem; }

  .toast {
    position: fixed; bottom: calc(20px + env(safe-area-inset-bottom, 0px)); left: 50%; transform: translateX(-50%);
    background: var(--ink); color: var(--paper); padding: 10px 18px; border-radius: var(--radius); font-size: .86rem; z-index: 200;
  }

  /* subject tag */
  .subject-tag {
    font-size: .7rem; border: 1px solid var(--gold); color: var(--gold); background: var(--gold-soft);
    padding: 2px 8px; border-radius: var(--radius); margin-left: 8px; font-weight: 500; white-space: nowrap;
  }

  /* image upload + media */
  .img-upload { display: inline-block; }
  .img-preview-wrap { position: relative; display: inline-block; margin-top: 6px; }
  .img-preview-wrap img { display: block; max-width: 220px; max-height: 150px; border: 1px solid var(--line); border-radius: var(--radius); object-fit: contain; background: var(--paper); }
  .img-remove-btn {
    position: absolute; top: -8px; right: -8px; background: var(--accent); color: #fff; border: none;
    border-radius: 50%; width: 22px; height: 22px; cursor: pointer; font-size: .85rem; line-height: 1;
  }
  .img-pick-label { cursor: pointer; }
  .option-image-row { margin-top: 8px; }
  .q-media img, .exp-media img { display: block; max-width: 100%; width: auto; max-height: 340px; border: 1px solid var(--line); border-radius: var(--radius); margin: 4px 0 16px; background: var(--card-bg); }
  .opt-media img { display: block; max-width: 100%; width: auto; max-height: 160px; border: 1px solid var(--line); border-radius: var(--radius); margin-top: 8px; background: var(--card-bg); }
  .mjx-container { font-size: 1em !important; }