:root {
    --azul: #4f7cff;
    --morado: #9b5de5;
    --rosa: #f15bb5;
    --fondo: #0f1220;
    --panel: #171b2e;
    --panel-2: #1e2338;
    --borde: #2b3152;
    --texto: #e8eaf6;
    --texto-tenue: #a4a9c9;
    --code-bg: #121524;
  }
  * { box-sizing: border-box; }
  html { scroll-behavior: smooth; }
  body {
    font-family: -apple-system, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    color: var(--texto); line-height: 1.7; font-size: 16px; margin: 0;
    background: var(--fondo);
  }

  /* ---------- Portada ---------- */
  .portada {
    min-height: 100vh; display: flex; flex-direction: column;
    justify-content: center; align-items: center; text-align: center;
    background:
      radial-gradient(circle at 20% 20%, rgba(155,93,229,.35), transparent 55%),
      radial-gradient(circle at 80% 30%, rgba(241,91,181,.28), transparent 50%),
      radial-gradient(circle at 50% 90%, rgba(79,124,255,.35), transparent 55%),
      linear-gradient(160deg, #12142a 0%, #191d3a 55%, #10122a 100%);
    color: #fff; padding: 60px 24px; position: relative; overflow: hidden;
  }
  .portada .emoji {
    font-size: 72px; margin-bottom: 18px;
    filter: drop-shadow(0 8px 24px rgba(0,0,0,.35));
  }
  .portada h1 {
    font-size: clamp(32px, 5vw, 52px); margin: 0 0 18px; line-height: 1.15;
    max-width: 780px; font-weight: 800; letter-spacing: -0.5px;
    color: #ffffff;
    text-shadow: 0 4px 30px rgba(0,0,0,.45);
  }
  .portada .sub {
    font-size: clamp(16px, 2vw, 20px); max-width: 560px; margin-bottom: 34px;
    color: #f1f2fb;
    text-shadow: 0 2px 12px rgba(0,0,0,.4);
  }
  .portada .meta {
    font-size: 14px; color: #dcdeef;
    border-top: 1px solid rgba(255,255,255,.25); padding-top: 20px;
    display: flex; gap: 10px; flex-wrap: wrap; justify-content: center; max-width: 520px;
  }
  .portada .meta span {
    background: rgba(255,255,255,.1); padding: 6px 14px; border-radius: 999px;
    border: 1px solid rgba(255,255,255,.18);
  }
  .btn-empezar {
    margin: 40px 0 32px; padding: 16px 38px; font-size: 17px; font-weight: 700;
    color: #fff; background: linear-gradient(135deg, var(--azul), var(--morado));
    border: none; border-radius: 999px; cursor: pointer;
    box-shadow: 0 10px 30px rgba(79,124,255,.45);
    transition: transform .18s ease, box-shadow .18s ease;
  }
  .btn-empezar:hover { transform: translateY(-2px); box-shadow: 0 14px 36px rgba(79,124,255,.55); }
  .btn-empezar:active { transform: translateY(0); }
  .scroll-hint {
    position: absolute; bottom: 28px; left: 50%; transform: translateX(-50%);
    color: rgba(255,255,255,.7); font-size: 13px; display: flex; flex-direction: column;
    align-items: center; gap: 6px; animation: rebote 2s infinite;
  }
  @keyframes rebote { 0%,100% { transform: translate(-50%,0); } 50% { transform: translate(-50%,8px); } }

  /* ---------- Layout app ---------- */
  .app { display: none; }
  .app.activa { display: grid; grid-template-columns: 300px 1fr; min-height: 100vh; }

  /* Sidebar */
  .sidebar {
    background: var(--panel); border-right: 1px solid var(--borde);
    padding: 20px 14px 40px; overflow-y: auto; max-height: 100vh; position: sticky; top: 0;
  }
  .sidebar-header {
    display: flex; align-items: center; gap: 10px; padding: 6px 8px 18px;
    border-bottom: 1px solid var(--borde); margin-bottom: 14px;
  }
  .sidebar-header .logo { font-size: 22px; }
  .sidebar-header .titulo { font-weight: 700; font-size: 14px; line-height: 1.3; color: var(--texto); }
  .progreso-global {
    margin: 0 8px 18px; padding: 12px 14px; background: var(--panel-2);
    border-radius: 12px; border: 1px solid var(--borde);
  }
  .progreso-global .label { font-size: 12px; color: var(--texto-tenue); margin-bottom: 8px; display: flex; justify-content: space-between; }
  .progreso-global .barra-fondo { height: 6px; background: #2a2f4d; border-radius: 999px; overflow: hidden; }
  .progreso-global .barra { height: 100%; width: 0%; border-radius: 999px;
    background: linear-gradient(90deg, var(--azul), var(--morado), var(--rosa));
    transition: width .3s ease; }

  .nav-modulo h3 {
    font-size: 11px; text-transform: uppercase; letter-spacing: .8px;
    color: var(--texto-tenue); margin: 18px 8px 8px; font-weight: 700;
  }
  .nav-modulo ul { list-style: none; margin: 0; padding: 0; }
  .nav-leccion {
    width: 100%; display: flex; align-items: center; gap: 10px;
    text-align: left; background: none; border: none; color: var(--texto-tenue);
    padding: 9px 8px; border-radius: 8px; cursor: pointer; font-size: 13.5px;
    transition: background .15s ease, color .15s ease;
  }
  .nav-leccion:hover { background: var(--panel-2); color: var(--texto); }
  .nav-leccion.activa { background: linear-gradient(90deg, rgba(79,124,255,.18), rgba(155,93,229,.12)); color: #fff; font-weight: 600; }
  .nav-leccion.completa .nav-num { background: linear-gradient(135deg, var(--azul), var(--morado)); color: #fff; }
  .nav-num {
    flex: 0 0 auto; width: 24px; height: 24px; border-radius: 50%;
    background: #2a2f4d; color: var(--texto-tenue); font-size: 10.5px; font-weight: 700;
    display: flex; align-items: center; justify-content: center;
  }
  .nav-titulo { overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }

  /* Contenido principal */
  .contenido { padding: 0; max-width: 100%; }
  .topbar {
    position: sticky; top: 0; z-index: 5; display: flex; align-items: center; gap: 14px;
    padding: 14px 28px; background: rgba(15,18,32,.85); backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--borde);
  }
  .topbar-menu-btn {
    display: none; background: var(--panel-2); border: 1px solid var(--borde); color: var(--texto);
    width: 38px; height: 38px; border-radius: 10px; font-size: 16px; cursor: pointer;
  }
  .topbar .ruta { font-size: 13px; color: var(--texto-tenue); }
  .topbar .ruta strong { color: var(--texto); }

  .unidad { display: none; padding: 40px 48px 60px; max-width: 820px; margin: 0 auto; }
  .unidad.activa { display: block; animation: aparecer .35s ease; }
  @keyframes aparecer { from { opacity: 0; transform: translateY(6px); } to { opacity: 1; transform: translateY(0); } }

  .unidad-progreso { display: flex; gap: 6px; margin-bottom: 32px; }
  .unidad-progreso-barra { display: flex; gap: 6px; width: 100%; }
  .unidad-progreso .seg {
    height: 5px; flex: 1; background: #2a2f4d; border-radius: 999px; overflow: hidden;
  }
  .unidad-progreso .seg > i {
    display: block; height: 100%; width: 0%; border-radius: 999px;
    background: linear-gradient(90deg, var(--azul), var(--rosa)); transition: width .25s ease;
  }

  .step { display: none; }
  .step.activo { display: block; animation: aparecer .3s ease; }

  .step-body h1 { font-size: 30px; color: #fff; margin: 0 0 20px; font-weight: 800; letter-spacing: -.3px; }
  .step-body h2 {
    font-size: 21px; color: #cdd3ff; margin-top: 0; margin-bottom: 18px; font-weight: 700;
    padding-bottom: 10px; border-bottom: 1px solid var(--borde);
  }
  .step-body h3 { font-size: 17px; color: #b8a4ff; margin-top: 1.4em; }
  .step-body p, .step-body li { font-size: 16px; color: var(--texto); }
  .step-body p { margin: 1em 0; }
  .step-body strong { color: #fff; }
  .step-body ul, .step-body ol { padding-left: 1.4em; }
  .step-body li { margin: .4em 0; }

  .step-body code {
    font-family: "SF Mono", Menlo, Consolas, monospace;
    background: rgba(241,91,181,.14); padding: 2px 7px; border-radius: 5px;
    font-size: 14px; color: #ff9de2;
  }
  .step-body pre {
    background: var(--code-bg); color: #e0e0e0; padding: 18px 20px;
    border-radius: 12px; overflow-x: auto; font-size: 14px; line-height: 1.6;
    border: 1px solid var(--borde); margin: 1.3em 0;
    box-shadow: 0 8px 24px rgba(0,0,0,.25);
  }
  .step-body pre code { background: none; color: #dcdfef; padding: 0; font-size: 14px; }
  .step-body table { border-collapse: collapse; width: 100%; margin: 1.3em 0; font-size: 14.5px; }
  .step-body th, .step-body td { border: 1px solid var(--borde); padding: 10px 14px; text-align: left; }
  .step-body th { background: var(--panel-2); color: #cdd3ff; }
  .step-body tr:nth-child(even) td { background: rgba(255,255,255,.02); }
  .step-body blockquote {
    border-left: 4px solid var(--azul); background: var(--panel-2);
    margin: 1.3em 0; padding: 12px 18px; color: var(--texto-tenue); font-style: italic;
    border-radius: 0 10px 10px 0;
  }
  .step-body a { color: #7ea6ff; text-decoration: underline; text-decoration-color: rgba(126,166,255,.35); }
  .step-body a:hover { text-decoration-color: #7ea6ff; }
  .step-body hr { border: none; border-top: 1px solid var(--borde); margin: 2em 0; }

  /* Navegación de steps */
  .step-nav {
    display: flex; align-items: center; justify-content: space-between;
    margin-top: 44px; padding-top: 24px; border-top: 1px solid var(--borde); gap: 16px;
  }
  .btn-step {
    display: flex; align-items: center; gap: 8px; padding: 12px 20px;
    border-radius: 12px; border: 1px solid var(--borde); background: var(--panel-2);
    color: var(--texto); font-size: 14.5px; font-weight: 600; cursor: pointer;
    transition: background .15s ease, transform .15s ease, border-color .15s ease;
  }
  .btn-step:hover:not(:disabled) { background: #262c4a; border-color: #3a4270; transform: translateY(-1px); }
  .btn-step:disabled { opacity: .35; cursor: default; }
  .btn-next {
    background: linear-gradient(135deg, var(--azul), var(--morado)); border: none; color: #fff;
    box-shadow: 0 6px 18px rgba(79,124,255,.35);
  }
  .btn-next:hover:not(:disabled) { box-shadow: 0 8px 22px rgba(79,124,255,.45); }
  .btn-arrow { font-size: 16px; }
  .step-contador { font-size: 13px; color: var(--texto-tenue); font-variant-numeric: tabular-nums; white-space: nowrap; }

  .overlay { display: none; position: fixed; inset: 0; background: rgba(0,0,0,.5); z-index: 15; }
  .overlay.visible { display: block; }

  /* Responsive */
  @media (max-width: 880px) {
    .app.activa { grid-template-columns: 1fr; }
    .sidebar {
      position: fixed; inset: 0 auto 0 0; width: 82vw; max-width: 320px;
      transform: translateX(-100%); transition: transform .25s ease; z-index: 20;
      box-shadow: 20px 0 40px rgba(0,0,0,.4);
    }
    .sidebar.abierta { transform: translateX(0); }
    .topbar-menu-btn { display: block; }
    .unidad { padding: 28px 20px 48px; }
    .step-body h1 { font-size: 25px; }
  }

  ::-webkit-scrollbar { width: 10px; height: 10px; }
  ::-webkit-scrollbar-track { background: transparent; }
  ::-webkit-scrollbar-thumb { background: #2f3557; border-radius: 999px; }
  ::-webkit-scrollbar-thumb:hover { background: #3d456e; }