/* Visor de cursos: aprende, curso_gratis y course_preview */
  .learn {
    padding-top: calc(64px + var(--space-xl));
    padding-bottom: var(--space-3xl);
  }

  .learn-header { margin-bottom: var(--space-xl); }
  .learn-header__eyebrow {
    font-family: var(--font-mono);
    font-size: 0.75rem;
    color: var(--color-secondary);
    margin: 0 0 var(--space-xs) 0;
    letter-spacing: 0.04em;
  }
  .learn-header__title {
    font-family: var(--font-sans);
    font-size: clamp(1.5rem, 3vw, 2.25rem);
    font-weight: 700;
    color: var(--color-on-background);
    margin: 0 0 var(--space-md) 0;
    letter-spacing: -0.015em;
  }
  .learn-header__progress {
    display: flex;
    align-items: center;
    gap: var(--space-md);
    flex-wrap: wrap;
  }
  .learn-progress {
    flex: 1;
    min-width: 200px;
    height: 6px;
    background: var(--color-surface-alt);
    border-radius: var(--radius-full);
    overflow: hidden;
  }
  .learn-progress__bar {
    height: 100%;
    background: var(--color-primary);
    box-shadow: 0 0 12px rgba(37, 99, 235, 0.4);
    transition: width var(--dur-slow) var(--ease-out-quart);
  }
  .learn-progress__label {
    font-family: var(--font-mono);
    font-size: 0.8125rem;
    color: var(--color-on-surface-muted);
  }

  .learn-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: var(--space-xl);
  }
  @media (min-width: 1024px) {
    .learn-grid {
      grid-template-columns: 320px 1fr;
      gap: var(--space-2xl);
      align-items: start;
    }
  }

  /* Índice (.learn-aside): columna sticky en desktop; en mobile es un panel
     inferior que abre la barra .learn-bar (ver _learn_mobilebar.html y
     _learn_nav_script.html). Así el contenido de la lección queda primero. */
  .learn-aside {
    display: flex;
    flex-direction: column;
    gap: var(--space-md);
    min-width: 0;
  }
  .learn-main { min-width: 0; }
  .learn-aside__sheet-head { display: none; }

  @media (min-width: 1024px) {
    .learn-aside {
      position: sticky;
      top: 80px;
      max-height: calc(100vh - 100px);
      overflow-y: auto;
    }
    .learn-bar, .learn-backdrop { display: none !important; }
  }

  @media (max-width: 1023px) {
    .learn-aside {
      position: fixed;
      left: 0;
      right: 0;
      bottom: 0;
      z-index: 60;
      max-height: 85vh;
      max-height: 85dvh;
      overflow-y: auto;
      overscroll-behavior: contain;
      gap: var(--space-sm);
      padding: 0 var(--space-md) calc(var(--space-lg) + env(safe-area-inset-bottom, 0px));
      background: var(--color-background);
      border-top: 1px solid var(--color-border);
      border-radius: var(--radius-lg) var(--radius-lg) 0 0;
      box-shadow: 0 -12px 40px rgba(0, 0, 0, 0.45);
      transform: translateY(100%);
      visibility: hidden;
      transition: transform var(--dur-base) var(--ease-out-quart), visibility 0s linear var(--dur-base);
    }
    .learn-aside.is-open {
      transform: none;
      visibility: visible;
      transition: transform var(--dur-base) var(--ease-out-quart), visibility 0s;
    }
    .learn-aside__sheet-head {
      position: sticky;
      top: 0;
      z-index: 1;
      display: flex;
      align-items: center;
      justify-content: space-between;
      gap: var(--space-md);
      padding: var(--space-md) 0 var(--space-sm);
      background: var(--color-background);
    }
    .learn-aside__sheet-title {
      margin: 0;
      font-family: var(--font-mono);
      font-size: 0.8125rem;
      letter-spacing: 0.04em;
      color: var(--color-secondary);
    }
    .learn-aside__close {
      display: inline-flex;
      align-items: center;
      justify-content: center;
      width: 40px;
      height: 40px;
      border: 1px solid var(--color-border);
      border-radius: var(--radius-md);
      background: var(--color-surface);
      color: var(--color-on-surface);
      cursor: pointer;
    }
    .learn-backdrop {
      position: fixed;
      inset: 0;
      z-index: 55;
      background: rgba(0, 0, 0, 0.6);
    }
    body.learn-index-open { overflow: hidden; }
    /* <main> (pypro.css: z-index 2) es el contexto de apilamiento del panel
       y el backdrop; con el panel abierto lo subimos sobre el nav (50) para
       que el backdrop también lo cubra y tocar arriba cierre el índice. */
    body.learn-index-open #main { z-index: 51; }

    /* Barra de lección: sticky bajo el nav fijo (64px). */
    .learn-bar {
      position: sticky;
      top: 64px;
      z-index: 40;
      display: flex;
      align-items: center;
      gap: var(--space-xs);
      margin: 0 calc(-1 * var(--space-md)) var(--space-md);
      padding: 8px var(--space-md);
      background: var(--color-background);
      border-top: 1px solid var(--color-border);
      border-bottom: 1px solid var(--color-border);
    }
    .learn-bar__step {
      flex-shrink: 0;
      display: inline-flex;
      align-items: center;
      justify-content: center;
      width: 40px;
      height: 40px;
      border-radius: var(--radius-md);
      color: var(--color-on-background);
      text-decoration: none;
    }
    .learn-bar__step:hover { background: var(--color-surface); }
    .learn-bar__step.is-disabled { color: var(--color-on-surface-muted); opacity: 0.35; }
    .learn-bar__pos {
      flex: 1;
      min-width: 0;
      margin: 0;
      display: flex;
      flex-direction: column;
      line-height: 1.25;
    }
    .learn-bar__count {
      font-family: var(--font-mono);
      font-size: 0.7rem;
      letter-spacing: 0.04em;
      color: var(--color-secondary);
    }
    .learn-bar__title {
      font-size: 0.8125rem;
      font-weight: 600;
      color: var(--color-on-background);
      white-space: nowrap;
      overflow: hidden;
      text-overflow: ellipsis;
    }
    .learn-bar__index {
      flex-shrink: 0;
      display: inline-flex;
      align-items: center;
      gap: 6px;
      height: 40px;
      padding: 0 12px;
      border: 1px solid var(--color-border-strong);
      border-radius: var(--radius-md);
      background: var(--color-surface);
      color: var(--color-on-background);
      font-size: 0.8125rem;
      font-weight: 600;
      cursor: pointer;
    }

    /* #leccion: al llegar por anchor, que el título no quede bajo nav + barra. */
    .learn-lesson-head { scroll-margin-top: calc(64px + 58px + var(--space-md)); }
  }
  @media (min-width: 1024px) {
    .learn-lesson-head { scroll-margin-top: calc(64px + var(--space-lg)); }
  }
  @media (prefers-reduced-motion: reduce) {
    .learn-aside, .learn-aside.is-open { transition: none; }
  }

  .learn-section {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    padding: var(--space-md) var(--space-md);
  }
  .learn-section[open] { background: var(--color-surface); }
  .learn-section__head {
    cursor: pointer;
    list-style: none;
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    font-weight: 600;
    color: var(--color-on-background);
  }
  .learn-section__head::-webkit-details-marker { display: none; }
  .learn-section__num {
    font-family: var(--font-mono);
    font-size: 0.75rem;
    color: var(--color-secondary);
  }
  .learn-section__title { font-size: 0.9375rem; flex: 1; }
  .learn-section__meter {
    flex-shrink: 0;
    width: 48px;
    height: 4px;
    background: var(--color-divider);
    border-radius: var(--radius-full);
    overflow: hidden;
  }
  .learn-section__meter-bar {
    display: block;
    height: 100%;
    background: linear-gradient(90deg, var(--color-primary), var(--color-secondary));
    border-radius: var(--radius-full);
    transition: width var(--dur-base) var(--ease-out-quart);
  }
  .learn-section__pct {
    font-family: var(--font-mono);
    font-size: 0.7rem;
    color: var(--color-on-surface-muted);
    flex-shrink: 0;
  }

  .learn-lesson-list {
    list-style: none;
    margin: var(--space-sm) 0 0 0;
    padding: 0;
    display: flex;
    flex-direction: column;
    gap: 2px;
  }
  .learn-lesson {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    padding: 8px 10px;
    border-radius: var(--radius-sm);
    color: var(--color-on-surface);
    text-decoration: none;
    font-size: 0.875rem;
    border: 1px solid transparent;
    transition: background var(--dur-base) var(--ease-out-quart), border-color var(--dur-base) var(--ease-out-quart);
  }
  .learn-lesson:hover {
    background: var(--color-surface-alt);
    color: var(--color-on-background);
  }
  .learn-lesson--current {
    background: var(--color-primary-container);
    border-color: var(--color-primary);
    color: var(--color-secondary);
  }
  .learn-lesson--current:hover { background: var(--color-primary-container); }
  .learn-lesson--done .learn-lesson__icon { color: var(--color-success); }
  .learn-lesson__icon {
    flex-shrink: 0;
    width: 16px;
    text-align: center;
    font-family: var(--font-mono);
    color: var(--color-on-surface-muted);
  }
  .learn-lesson__title { flex: 1; }
  .learn-lesson__preview {
    font-family: var(--font-mono);
    font-size: 0.65rem;
    background: var(--color-primary-container);
    color: var(--color-secondary);
    padding: 2px 6px;
    border-radius: var(--radius-sm);
    letter-spacing: 0.04em;
    text-transform: uppercase;
  }
  .learn-lesson__dur {
    font-family: var(--font-mono);
    font-size: 0.7rem;
    color: var(--color-on-surface-muted);
  }

  .learn-main {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-lg);
    padding: var(--space-xl);
  }
  @media (min-width: 768px) {
    .learn-main { padding: var(--space-2xl); }
  }

  .learn-lesson-head { margin-bottom: var(--space-xl); }
  .learn-lesson-head__meta {
    display: flex;
    flex-wrap: wrap;
    gap: var(--space-sm);
    align-items: center;
    margin-bottom: var(--space-md);
  }
  .learn-lesson-head__dur {
    font-family: var(--font-mono);
    font-size: 0.8125rem;
    color: var(--color-on-surface-muted);
  }
  .learn-lesson-head__title {
    font-family: var(--font-sans);
    font-size: clamp(1.25rem, 2.5vw, 1.75rem);
    font-weight: 700;
    color: var(--color-on-background);
    margin: 0 0 var(--space-xs) 0;
    letter-spacing: -0.015em;
  }
  .learn-lesson-head__sub {
    font-size: 0.875rem;
    color: var(--color-on-surface-muted);
    margin: 0;
  }

  .learn-lesson-body { margin-bottom: var(--space-xl); }

  /* `position: relative` viene fusionado del bloque de progress-overlay de
     aprende.html, que antes del refactor solo se emitía en el modo
     interactivo. Al fusionarse aquí queda en la regla base .learn-video y
     es inerte en curso_gratis/course_preview, que no tienen overlay. */
  .learn-video {
    aspect-ratio: 16 / 9;
    background: var(--color-code-bg);
    border-radius: var(--radius-md);
    overflow: hidden;
    margin-bottom: var(--space-lg);
    border: 1px solid var(--color-border);
    position: relative;
  }
  .learn-video iframe {
    width: 100%;
    height: 100%;
    display: block;
    border: 0;
  }
  .learn-video__progress {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    padding: var(--space-sm) var(--space-md);
    background: var(--color-surface-alt);
    border-top: 1px solid var(--color-border);
    font-size: 0.8125rem;
    color: var(--color-on-surface-muted);
  }
  .learn-video__progress-bar {
    display: inline-block;
    flex: 1;
    height: 4px;
    border-radius: 2px;
    background: linear-gradient(to right, var(--color-primary), var(--color-secondary));
    transition: width 0.4s ease-out;
    min-width: 0;
    position: relative;
  }
  .learn-video__progress-label { white-space: nowrap; min-width: 5.5em; text-align: right; }

  .learn-video-placeholder {
    aspect-ratio: 16 / 9;
    background: var(--color-code-bg);
    border: 1px dashed var(--color-border-strong);
    border-radius: var(--radius-md);
    display: flex;
    align-items: center;
    justify-content: center;
    margin-bottom: var(--space-lg);
  }
  .learn-video-placeholder__inner {
    text-align: center;
    color: var(--color-on-surface-muted);
  }
  .learn-video-placeholder__inner p { margin: 4px 0; }

  .learn-audio {
    display: block;
    width: 100%;
    margin-bottom: var(--space-lg);
  }

  .learn-content { padding: 0; }

  /* "En este video": resumen y código del video (_video_extras.html) */
  .video-extras {
    margin: 0 0 var(--space-xl);
    display: flex;
    flex-direction: column;
    gap: var(--space-md);
  }
  .video-extras__title {
    font-family: var(--font-mono);
    font-size: 0.75rem;
    letter-spacing: 0.08em;
    text-transform: uppercase;
    color: var(--color-on-surface-muted);
    margin: 0;
  }
  .video-extras__summary {
    margin: 0;
    padding: var(--space-md) var(--space-lg) var(--space-md) calc(var(--space-lg) + 1em);
    background: var(--color-surface-alt);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    color: var(--color-on-surface);
    line-height: 1.6;
  }
  .video-extras__summary li + li { margin-top: var(--space-xs); }
  .video-code {
    margin: 0;
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    overflow: hidden;
    background: var(--color-code-bg);
  }
  .video-code__bar {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: var(--space-sm);
    padding: 6px 8px 6px var(--space-md);
    border-bottom: 1px solid var(--color-border);
    font-family: var(--font-mono);
    font-size: 0.75rem;
    color: var(--color-on-surface-muted);
  }
  .video-code__name { overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
  .video-code__copy {
    flex: none;
    min-height: 32px;
    padding: 4px 12px;
    border: 1px solid var(--color-border);
    border-radius: var(--radius-sm);
    background: var(--color-surface);
    color: var(--color-on-surface);
    font: inherit;
    cursor: pointer;
  }
  .video-code__copy:hover { border-color: var(--color-secondary); color: var(--color-on-background); }
  .video-code__copy:focus-visible { outline: 2px solid var(--color-secondary); outline-offset: 2px; }
  .video-code__pre {
    margin: 0;
    padding: var(--space-md);
    overflow-x: auto;
    font-family: var(--font-mono);
    font-size: 0.8125rem;
    line-height: 1.6;
    tab-size: 4;
    white-space: pre;
    background: transparent;
  }
  /* El tema de Prism trae su propio fondo y márgenes: el bloque usa el de terminal. */
  .video-code pre.video-code__pre,
  .video-code__pre code[class*="language-"] {
    background: transparent !important;
    margin: 0 !important;
    border: 0;
    box-shadow: none;
    text-shadow: none;
  }
  .video-code__pre code[class*="language-"] { padding: 0; font-size: inherit; }

  .learn-resources {
    margin-top: var(--space-xl);
    padding: var(--space-lg);
    background: var(--color-surface-alt);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
  }
  .learn-resources__title {
    font-family: var(--font-mono);
    font-size: 0.75rem;
    letter-spacing: 0.08em;
    text-transform: uppercase;
    color: var(--color-on-surface-muted);
    margin: 0 0 var(--space-md) 0;
  }
  .learn-resources__list {
    list-style: none;
    padding: 0;
    margin: 0;
    display: flex;
    flex-direction: column;
    gap: var(--space-xs);
  }
  .learn-resource {
    display: flex;
    align-items: center;
    gap: var(--space-md);
    padding: 10px 12px;
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-sm);
    color: var(--color-on-surface);
    text-decoration: none;
    font-size: 0.9375rem;
    transition: border-color var(--dur-base) var(--ease-out-quart), color var(--dur-base) var(--ease-out-quart);
  }
  .learn-resource:hover {
    border-color: var(--color-secondary);
    color: var(--color-on-background);
  }
  .learn-resource__icon {
    font-family: var(--font-mono);
    color: var(--color-secondary);
    flex-shrink: 0;
    width: 20px;
    text-align: center;
  }
  .learn-resource__title { flex: 1; }
  .learn-resource__meta {
    font-family: var(--font-mono);
    font-size: 0.75rem;
    color: var(--color-on-surface-muted);
  }

  /* ============ Review ============ */
  .review-block {
    margin-top: var(--space-xl);
    padding: var(--space-lg);
    background: linear-gradient(135deg, rgba(245, 158, 11, 0.06), var(--color-surface-alt));
    border: 1px solid rgba(245, 158, 11, 0.3);
    border-radius: var(--radius-md);
  }
  .review-block__title {
    font-family: var(--font-sans);
    font-size: 1.0625rem;
    font-weight: 600;
    color: var(--color-on-background);
    margin: 0 0 4px 0;
  }
  .review-block__sub {
    font-size: 0.875rem;
    color: var(--color-on-surface-muted);
    margin: 0 0 var(--space-md) 0;
  }
  .review-form {
    display: flex;
    flex-direction: column;
    gap: var(--space-sm);
    align-items: flex-start;
  }
  .rating-input { display: flex; gap: 2px; }
  .rating-input__star {
    cursor: pointer;
    font-size: 1.5rem;
    color: var(--color-on-surface-muted);
    transition: color var(--dur-base) var(--ease-out-quart);
  }
  .rating-input__star input { position: absolute; opacity: 0; pointer-events: none; }
  .rating-input__star:has(input:checked) { color: var(--color-warning); }
  .rating-input__star:has(input:checked) ~ .rating-input__star { color: var(--color-on-surface-muted); }
  .rating-input:hover .rating-input__star { color: var(--color-warning); }
  .rating-input__star:hover ~ .rating-input__star { color: var(--color-on-surface-muted); }
  .sr-only {
    position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px;
    overflow: hidden; clip: rect(0, 0, 0, 0); white-space: nowrap; border: 0;
  }

  /* ============ Q&A ============ */
  .qa {
    margin-top: var(--space-xl);
    padding-top: var(--space-xl);
    border-top: 1px solid var(--color-divider);
  }
  .qa__head { margin-bottom: var(--space-lg); }
  .qa__title {
    font-family: var(--font-sans);
    font-size: 1.125rem;
    font-weight: 600;
    color: var(--color-on-background);
    margin: 0 0 4px 0;
  }
  .qa__sub {
    font-size: 0.875rem;
    color: var(--color-on-surface-muted);
    margin: 0;
  }

  .qa-ask {
    background: var(--color-surface-alt);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    padding: var(--space-md) var(--space-lg);
    display: flex;
    flex-direction: column;
    gap: var(--space-sm);
    margin-bottom: var(--space-xl);
  }
  .qa-ask__row {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: var(--space-md);
    flex-wrap: wrap;
  }
  .qa-ask__ts {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    font-family: var(--font-mono);
    font-size: 0.75rem;
    color: var(--color-on-surface-muted);
  }
  .qa-ask__ts-input {
    width: 80px;
    padding: 6px 10px;
  }

  .qa-list {
    list-style: none;
    padding: 0;
    margin: 0;
    display: flex;
    flex-direction: column;
    gap: var(--space-md);
  }
  .qa-thread {
    background: var(--color-surface-alt);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    padding: var(--space-lg);
  }
  .qa-thread--pinned {
    border-color: var(--color-warning);
    background: rgba(245, 158, 11, 0.06);
  }
  .qa-thread__head {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: var(--space-md);
    margin-bottom: var(--space-sm);
  }
  .qa-thread__meta {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    flex-wrap: wrap;
    font-size: 0.8125rem;
  }
  .qa-author { font-weight: 600; color: var(--color-on-background); }
  .qa-date { color: var(--color-on-surface-muted); font-family: var(--font-mono); font-size: 0.75rem; }
  .qa-ts {
    font-family: var(--font-mono);
    font-size: 0.75rem;
    color: var(--color-secondary);
    text-decoration: none;
    background: var(--color-primary-container);
    padding: 2px 8px;
    border-radius: var(--radius-sm);
  }
  .qa-ts:hover { color: var(--color-on-background); }

  .qa-badge {
    font-family: var(--font-mono);
    font-size: 0.65rem;
    padding: 2px 6px;
    border-radius: var(--radius-sm);
    letter-spacing: 0.06em;
    text-transform: uppercase;
  }
  .qa-badge--instructor { background: var(--color-primary); color: var(--color-on-primary); }
  .qa-badge--pinned { background: rgba(245, 158, 11, 0.15); color: var(--color-warning); }

  .qa-upvote-form { margin: 0; }
  .qa-upvote {
    background: transparent;
    border: 1px solid var(--color-border);
    color: var(--color-on-surface);
    padding: 4px 10px;
    border-radius: var(--radius-sm);
    font-family: var(--font-mono);
    font-size: 0.75rem;
    cursor: pointer;
    transition: border-color var(--dur-base) var(--ease-out-quart), color var(--dur-base) var(--ease-out-quart);
  }
  .qa-upvote:hover { border-color: var(--color-secondary); color: var(--color-secondary); }

  .qa-thread__title {
    font-weight: 600;
    color: var(--color-on-background);
    margin: 0 0 var(--space-xs) 0;
    font-size: 0.9375rem;
  }
  .qa-thread__body {
    color: var(--color-on-surface);
    font-size: 0.9375rem;
    margin-bottom: var(--space-md);
  }
  .qa-thread__body p:last-child { margin-bottom: 0; }

  .qa-replies {
    list-style: none;
    margin: var(--space-md) 0;
    padding: 0 0 0 var(--space-md);
    border-left: 2px solid var(--color-divider);
    display: flex;
    flex-direction: column;
    gap: var(--space-md);
  }
  .qa-reply {
    padding: var(--space-md);
    background: var(--color-surface);
    border-radius: var(--radius-sm);
    border: 1px solid var(--color-border);
  }
  .qa-reply--instructor {
    border-color: var(--color-primary);
    background: var(--color-primary-container);
  }
  .qa-reply__body { font-size: 0.9375rem; margin-top: 6px; }
  .qa-reply__body p:last-child { margin-bottom: 0; }

  .qa-reply-form {
    display: flex;
    flex-direction: column;
    gap: var(--space-sm);
    align-items: flex-start;
    margin-top: var(--space-md);
  }

  .learn-lesson-foot {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: var(--space-md);
    padding-top: var(--space-lg);
    border-top: 1px solid var(--color-divider);
  }
  .learn-complete-form { margin: 0; }

  /* ============ Quiz ============ */
  /* Quiz local (curso gratis): [hidden] debe ganarle a display de .btn/.quiz-* */
  .quiz-local [hidden] { display: none !important; }
  .quiz-intro {
    background: var(--color-surface-alt);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    padding: var(--space-md) var(--space-lg);
    margin-bottom: var(--space-xl);
  }
  .quiz-intro p { margin: 0; }
  .quiz-intro p + p { margin-top: 6px; }

  .quiz-list {
    list-style: none;
    padding: 0;
    margin: 0;
    display: flex;
    flex-direction: column;
    gap: var(--space-xl);
  }
  .quiz-question {
    background: var(--color-background);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    padding: var(--space-lg);
  }
  .quiz-question__text {
    font-size: 1rem;
    color: var(--color-on-background);
    margin: 0 0 var(--space-md) 0;
    line-height: 1.5;
  }
  .quiz-options {
    list-style: none;
    padding: 0;
    margin: 0;
    display: flex;
    flex-direction: column;
    gap: var(--space-xs);
  }
  .quiz-option {
    display: flex;
    align-items: flex-start;
    gap: var(--space-sm);
    padding: 10px 14px;
    border: 1px solid var(--color-border);
    border-radius: var(--radius-sm);
    background: var(--color-surface);
    color: var(--color-on-surface);
    font-size: 0.9375rem;
    line-height: 1.4;
  }
  .quiz-option--input {
    cursor: pointer;
    transition: border-color var(--dur-base) var(--ease-out-quart), background var(--dur-base) var(--ease-out-quart);
  }
  .quiz-option--input:hover {
    border-color: var(--color-border-strong);
    background: var(--color-surface-alt);
  }
  .quiz-option--input input[type="radio"] {
    margin-top: 3px;
    flex-shrink: 0;
    accent-color: var(--color-primary);
  }
  .quiz-option__marker {
    flex-shrink: 0;
    width: 18px;
    text-align: center;
    font-family: var(--font-mono);
    font-weight: 700;
    color: var(--color-on-surface-muted);
  }
  .quiz-option--correct {
    border-color: rgba(16, 185, 129, 0.5);
    background: rgba(16, 185, 129, 0.08);
    color: #6EE7B7;
  }
  .quiz-option--correct .quiz-option__marker { color: var(--color-success); }
  .quiz-option--wrong {
    border-color: rgba(239, 68, 68, 0.5);
    background: rgba(239, 68, 68, 0.08);
    color: #FCA5A5;
  }
  .quiz-option--wrong .quiz-option__marker { color: var(--color-error); }
  .quiz-option--chosen:not(.quiz-option--correct):not(.quiz-option--wrong) {
    border-color: var(--color-border-strong);
  }
  .quiz-question__explanation {
    margin: var(--space-md) 0 0 0;
    padding: var(--space-md);
    background: var(--color-surface-alt);
    border-left: 3px solid var(--color-secondary);
    border-radius: var(--radius-sm);
    font-size: 0.875rem;
    color: var(--color-on-surface);
    line-height: 1.55;
  }
  .quiz-actions {
    display: flex;
    flex-wrap: wrap;
    gap: var(--space-md);
    margin-top: var(--space-xl);
  }

  .quiz-result {
    margin-bottom: var(--space-xl);
    padding: var(--space-lg);
    border-radius: var(--radius-md);
    border: 1px solid var(--color-border);
  }
  .quiz-result--pass {
    border-color: rgba(16, 185, 129, 0.4);
    background: rgba(16, 185, 129, 0.06);
  }
  .quiz-result--fail {
    border-color: rgba(239, 68, 68, 0.4);
    background: rgba(239, 68, 68, 0.06);
  }
  .quiz-result__label {
    font-family: var(--font-mono);
    font-size: 0.75rem;
    color: var(--color-on-surface-muted);
    margin: 0 0 4px 0;
    letter-spacing: 0.04em;
  }
  .quiz-result__score {
    font-family: var(--font-sans);
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--color-on-background);
    margin: 0 0 8px 0;
  }
  .quiz-result--pass .quiz-result__score { color: var(--color-success); }
  .quiz-result--fail .quiz-result__score { color: var(--color-error); }
  .quiz-result__hint {
    font-size: 0.9375rem;
    color: var(--color-on-surface);
    margin: 0;
  }

/* ---- course_preview ---- */
  .preview-shell {
    padding-top: calc(64px + var(--space-2xl));
    padding-bottom: var(--space-3xl);
  }
  .preview-head { margin-bottom: var(--space-xl); }
  .preview-head__eyebrow {
    font-family: var(--font-mono);
    font-size: 0.8125rem;
    margin: 0 0 var(--space-sm) 0;
  }
  .preview-head__eyebrow a {
    color: var(--color-secondary);
    text-decoration: none;
  }
  .preview-head__title {
    font-family: var(--font-sans);
    font-size: clamp(1.5rem, 3vw, 2.25rem);
    font-weight: 700;
    color: var(--color-on-background);
    margin: 0 0 var(--space-sm) 0;
    letter-spacing: -0.015em;
  }
  .preview-head__sub {
    color: var(--color-on-surface-muted);
    font-size: 0.9375rem;
    display: flex;
    flex-wrap: wrap;
    gap: var(--space-sm);
    align-items: center;
  }

  .preview-body {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-lg);
    padding: var(--space-xl);
    margin-bottom: var(--space-xl);
  }
  @media (min-width: 768px) {
    .preview-body { padding: var(--space-2xl); }
  }

  .preview-cta {
    padding: var(--space-xl);
    background: linear-gradient(135deg, var(--color-primary-container), var(--color-surface-alt));
    border: 1px solid var(--color-primary);
    border-radius: var(--radius-lg);
    text-align: center;
  }
  .preview-cta__eyebrow {
    font-family: var(--font-mono);
    font-size: 0.75rem;
    letter-spacing: 0.08em;
    color: var(--color-secondary);
    margin: 0 0 var(--space-sm) 0;
  }
  .preview-cta__title {
    font-size: clamp(1.25rem, 2vw, 1.5rem);
    font-weight: 700;
    color: var(--color-on-background);
    margin: 0 0 var(--space-lg) 0;
  }
  .preview-cta__row {
    display: flex;
    flex-wrap: wrap;
    gap: var(--space-md);
    justify-content: center;
  }