body.is-ai .study>h1:first-child::before {
      content: "Beginner friendly · Build and ship today";
    }

    .study>h1 em,
    .topic-title em {
      color: var(--accent);
    }

    .viz-label {
      display: block;
      margin: 12px 0 6px;
      color: var(--muted);
      font-size: 12px;
      font-weight: 600;
      letter-spacing: 0.04em;
      text-transform: uppercase;
    }

    .viz-label:first-child {
      margin-top: 0;
    }

    .viz-stage.is-text {
      padding: 12px 14px;
      font-size: 16px;
      line-height: 1.6;
    }

    .viz-stage.is-text ul {
      margin: 6px 0;
      padding-left: 20px;
    }

    .viz-stage.is-text ol {
      margin: 6px 0;
      padding-left: 2.4rem;
    }

    .viz-hint,
    .placeholder {
      color: var(--muted);
      font-size: 12.5px;
      font-style: italic;
    }

    .tok {
      display: inline-block;
      margin: 2px;
      padding: 2px 7px;
      border-radius: 5px;
      font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
      font-size: 13px;
    }

    .prob-row {
      display: flex;
      align-items: center;
      gap: 10px;
      margin: 6px 0;
    }

    .prob-word {
      flex: none;
      width: 110px;
      font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
      font-size: 12.5px;
      text-align: right;
    }

    .prob-track {
      flex: 1;
      height: 18px;
      overflow: hidden;
      background: var(--surface-raised);
      border: 1px solid var(--line);
      border-radius: 4px;
    }

    .prob-fill {
      height: 100%;
      min-width: 2px;
      background: var(--accent);
    }

    .prob-pct {
      flex: none;
      width: 52px;
      font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
      font-size: 12px;
    }

    .mask-sent {
      margin: 6px 0 14px;
      font-family: Georgia, "Times New Roman", serif;
      font-size: 20px;
      text-align: center;
    }

    .mask-blank {
      display: inline-block;
      min-width: 110px;
      color: var(--accent-bright);
      border-bottom: 2px solid var(--accent);
      font-weight: 700;
    }

    .duo {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 12px;
    }

    .duo-side {
      display: flex;
      flex-direction: column;
      gap: 8px;
      padding: 12px 14px;
      background: var(--surface-raised);
      border: 1px solid var(--line);
      border-radius: 8px;
      text-align: center;
    }

    .duo-side.is-left {
      text-align: left;
    }

    .duo-who {
      color: var(--accent);
      font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
      font-size: 11px;
      font-weight: 700;
      letter-spacing: 0.06em;
      text-transform: uppercase;
    }

    .duo-resp {
      flex: 1;
      font-size: 16px;
      line-height: 1.6;
      white-space: pre-line;
    }

    .msg {
      margin: 8px 0;
      padding: 8px 12px;
      font-size: 16px;
      background: var(--surface-raised);
      border-left: 3px solid var(--line);
      border-radius: 0 6px 6px 0;
    }

    .msg b {
      display: block;
      color: var(--muted);
      font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
      font-size: 11px;
      letter-spacing: 0.06em;
      text-transform: uppercase;
    }

    .msg.thought {
      border-left-color: var(--blue);
    }

    .msg.action {
      border-left-color: var(--accent);
    }

    .msg.obs {
      border-left-color: var(--cyan);
    }

    .msg.answer {
      border-left-color: var(--green);
    }

    @media (max-width: 640px) {
      .duo {
        grid-template-columns: 1fr;
      }

      .prob-word {
        width: 84px;
      }
    }