/* ── Skill tree ─────────────────────────────────────────────────────── */
  .sk-domain { margin-bottom: 30px; }
  .sk-domain-title { font-size: 13px; font-weight: 800; letter-spacing: 0.16em;
    text-transform: uppercase; color: var(--gold); margin-bottom: 10px; }
  .sk-level { display: flex; align-items: flex-start; gap: 10px; margin-bottom: 10px; }
  .sk-level-label { flex: 0 0 44px; font-size: 10px; font-weight: 700; letter-spacing: 0.1em;
    color: var(--muted); text-transform: uppercase; padding-top: 12px; text-align: right; }
  .sk-level-nodes { display: flex; flex-wrap: wrap; gap: 8px; flex: 1; }
  .sk-node { background: var(--card); border: 1px solid var(--border); border-radius: var(--radius);
    padding: 8px 12px; cursor: pointer; min-width: 150px; max-width: 220px;
    transition: border-color 0.15s, transform 0.15s; }
  .sk-node:hover { transform: translateY(-1px); }
  .sk-node-name { font-size: 12.5px; font-weight: 600; color: var(--text); line-height: 1.3; }
  .sk-node-meta { font-size: 10px; color: var(--muted); margin-top: 3px; letter-spacing: 0.04em; }
  .sk-node.sk-locked { opacity: 0.45; cursor: pointer; }
  .sk-node.sk-locked:hover { transform: none; }
  .sk-node.sk-locked .sk-node-name { color: var(--muted); }
  .sk-node.sk-available { border-color: var(--subtle); }
  .sk-node.sk-available:hover { border-color: var(--teal); }
  .sk-node.sk-lesson { border-color: var(--gold-dim); background: var(--gold-bg); }
  .sk-node.sk-lesson .sk-node-name { color: var(--gold); }
  .sk-node.sk-practicing { border-color: var(--purple-dim); background: var(--purple-bg); }
  .sk-node.sk-practicing .sk-node-name { color: var(--purple); }
  .sk-node.sk-proficient { border-color: var(--green); }
  .sk-node.sk-proficient .sk-node-name { color: var(--green); }
  .sk-node.sk-mastered { border-color: var(--green); background: var(--green-bg);
    box-shadow: 0 0 0 1px var(--green); }
  .sk-node.sk-mastered .sk-node-name { color: var(--green); }
  .sk-prereq-list { display: flex; flex-direction: column; gap: 8px; margin-top: 12px; }
  .sk-prereq-row { display: flex; align-items: center; justify-content: space-between; gap: 12px;
    padding: 8px 12px; background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); }
  .sk-prereq-name { font-size: 13px; color: var(--text); }
  .sk-legend { display: flex; flex-wrap: wrap; gap: 14px; margin-bottom: 22px;
    font-size: 11px; color: var(--muted); letter-spacing: 0.04em; }
  .sk-legend span { display: inline-flex; align-items: center; gap: 5px; }
  .sk-dot { width: 9px; height: 9px; border-radius: 50%; display: inline-block; }
  /* Lesson markdown rendering (mdToDom output) */
  .sk-md { font-size: 14px; line-height: 1.65; color: var(--text); }
  /* Staged lesson player */
  .lsn-head { display: flex; align-items: center; justify-content: space-between;
    gap: 12px; margin-bottom: 4px; }
  .lsn-progress { display: flex; gap: 7px; }
  .lsn-dot { width: 9px; height: 9px; border-radius: 50%; background: var(--border);
    cursor: pointer; transition: background 200ms, transform 200ms; }
  .lsn-dot.on { background: var(--gold); transform: scale(1.3); }
  .lsn-dot.done { background: var(--gold-dim); }
  .lsn-stage-label { font-size: 11px; color: var(--muted); letter-spacing: 0.08em;
    text-transform: uppercase; white-space: nowrap; }
  .lsn-stage { animation: lsnIn 260ms cubic-bezier(0.16, 1, 0.3, 1); }
  @keyframes lsnIn { from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: none; } }
  .lsn-nav { display: flex; justify-content: space-between; gap: 12px; margin-top: 22px; }
  .lsn-reveal { margin-top: 14px; }
  @media (prefers-reduced-motion: reduce) { .lsn-stage { animation: none; } }
  .sk-md h1 { font-size: 21px; margin: 18px 0 10px; color: var(--gold); }
  .sk-md h2 { font-size: 17px; margin: 18px 0 8px; color: var(--text); }
  .sk-md h3, .sk-md h4 { font-size: 14.5px; margin: 14px 0 6px; color: var(--text); }
  .sk-md p { margin: 8px 0; }
  .sk-md ul, .sk-md ol { margin: 8px 0 8px 22px; }
  .sk-md li { margin: 3px 0; }
  .sk-md blockquote { border-left: 3px solid var(--gold-dim); margin: 10px 0;
    padding: 4px 14px; color: var(--muted); font-style: italic; }
  .sk-md code { background: var(--surface); border: 1px solid var(--border);
    border-radius: var(--radius); padding: 1px 5px; font-size: 12.5px; }
  .sk-md pre { background: var(--surface); border: 1px solid var(--border);
    border-radius: var(--radius); padding: 12px 14px; overflow-x: auto; margin: 10px 0; }
  .sk-md pre code { background: none; border: none; padding: 0; }
  .sk-md hr { border: none; border-top: 1px solid var(--border); margin: 18px 0; }
  .sk-md table { border-collapse: collapse; margin: 10px 0; }
  .sk-md th, .sk-md td { border: 1px solid var(--border); padding: 5px 12px; font-size: 13px; }
  .sk-md th { background: var(--surface); font-weight: 700; }
  .sk-md .sk-math-block { margin: 10px 0; text-align: center; }

  /* ── Mobile pass (teens on phones, 360–430px) ───────────────────────────
     Additive: scoped to small viewports so desktop layout is untouched. Goals:
     no horizontal overflow, >=44px touch targets, wrapping toggle groups,
     full-width problem cards/choices, and modals/sheets that fit the screen. */
  @media (max-width: 560px) {
    /* Practice screen: the serving-knob cluster (subject/Mode/Bias/focus) and
       dashboard/history shortcuts duplicate Home controls — mid-question on a
       phone they push the problem below the fold. Desktop keeps them. */
    #screen-practice .topbar-filters, #screen-practice #dashboard-btn,
    #screen-practice #history-btn { display: none; }
    /* Confidence strip: label on its own line, three full-height chips,
       no keyboard-shortcut badges (meaningless on touch). */
    .conf-strip { flex-wrap: wrap; inset: auto 0 0 0; height: auto; min-height: 100%;
      padding: 6px 0; }
    .conf-q { flex: 1 1 100%; align-self: auto; text-align: center; padding: 0 0 4px; }
    .conf-chip { min-height: 44px; font-size: 13px; }
    .conf-key { display: none; }
    .topbar { padding: 10px 12px; }
    /* Padding only. The `gap` this used to set was the small-screen half of the
       stacking bug described on .bs .home-wrap; the .bs rule now zeroes it, but
       leaving it here would keep misleading the next reader. */
    .home-wrap { padding: 18px 14px 40px; }
    .home-greet { font-size: 22px; }
    .home-train-controls { gap: 12px; }
    .home-ctrl { flex: 1 1 100%; }
    .home-family-toggle, #home-family-toggle, #home-mode-toggle,
    #home-diff-toggle, #login-family-toggle, #login-mode-toggle,
    #login-diff-toggle { flex-wrap: wrap; }
    .home-train-controls .toggle-group { width: 100%; }
    .home-focus-sel { width: 100%; }
    .toggle-btn { padding: 10px 14px; font-size: 13px; min-height: 44px; }
    .home-start-btn { min-height: 48px; }
    .login-box .filter-row { flex-direction: column; align-items: stretch; }
    .login-box .filter-row .filter-group { width: 100%; }
    .login-box .filter-row .toggle-group { flex-wrap: wrap; }
    .problem-card { padding: 22px 18px; border-radius: var(--radius); }
    .passage-block { padding: 14px 16px; font-size: 15px; }
    .stem-block { font-size: 16px; }
    .choice-btn { padding: 14px 16px; min-height: 48px; }
    .free-response { flex-direction: column; }
    .practice-body { padding: 16px 12px; gap: 16px; }
    .dv2-hero-stats { flex-wrap: wrap; gap: 12px; }
    .dv2-next-grid { grid-template-columns: 1fr; }
    .dv2-skill-grid { grid-template-columns: 1fr; }
    .btn-ghost { min-height: 44px; }
    .home-iconbtn { width: 44px; height: 44px; }
  }
  @media (max-width: 430px) {
    .home-greet { font-size: 20px; }
    .home-rating-pill { min-width: 78px; padding: 8px 12px; }
    .home-rating-pill .hr-val { font-size: 19px; }
    .home-streak { font-size: 16px; padding: 8px 12px; }
    .home-card { padding: 16px 14px; }
    .home-lb-handle { font-size: 13px; }
    .problem-card { padding: 18px 14px; }
    .problem-meta { gap: 6px; }
    .badge { font-size: 9px; padding: 3px 7px; }
    .login-title { font-size: 30px; }
    .login-box { padding: 0 16px; }
    /* Skill-tree lesson overlay + any fixed modal must fit narrow screens. */
    #skilltree-lesson > div { padding: 20px 16px; }
    .end-box { padding: 24px 16px; }
  }