* { box-sizing: border-box; margin: 0; padding: 0; }

    body {
      font-family: 'Inter', sans-serif;
      color: #1a1a1a;
      display: flex;
      flex-direction: column;
      height: 100vh;
    }

    /* HEADER */
    header {
      height: 70px;
      background: #1e1e1e;
      border-bottom: 1px solid #eee;
      display: flex;
      align-items: center;
      justify-content: space-between;
      padding: 0 30px;
    }

    header img { height: 32px; }

    .home-button { text-decoration: none; font-weight: 500; color: #fff; transition: color 0.2s; }
    .home-button:hover { color: #0070f3; }

    .lang-switch { display: flex; gap: 10px; }
    .lang-button {
      cursor: pointer;
      padding: 4px 8px;
      border: 1px solid #ccc;
      border-radius: 4px;
      background: #f9f9f9;
      transition: all 0.2s;
    }
    .lang-button.active { background: #0070f3; color: #fff; border-color: #0070f3; }

    /* CONTENEDOR GENERAL */
    .container { display: flex; flex: 1; overflow: hidden; }

    /* SIDEBAR */
    nav {
      width: 260px;
      background: #f9f9f9;
      padding: 25px;
      box-shadow: 2px 0 5px rgba(0,0,0,0.05);
      overflow-y: auto;
    }

    nav h2 { font-size: 1.4rem; margin-bottom: 20px; color: #111; }
    nav ul { list-style: none; }
    nav ul li { margin: 12px 0; }
    nav ul li a { text-decoration: none; color: #333; font-weight: 500; transition: color 0.2s; }
    nav ul li a:hover { color: #0070f3; }
    .active-link { color: #0070f3; font-weight: 600; }

    /* CONTENIDO */
    main {
      flex: 1;
      padding: 40px;
      overflow-y: auto;
      background: #fff;
      position: relative;
    }

    main::before {
      content: "";
      background: url('https://viewer.3dtwins.tech/puntero_3dtwinsStar.png') no-repeat center;
      opacity: 0.05;
      position: absolute;
      top: 0; left: 0; right: 0; bottom: 0;
      z-index: 0;
      pointer-events: none;
    }
    main > * { position: relative; z-index: 1; }

    h1 { font-size: 2rem; margin-bottom: 20px; }
    h2 { font-size: 1.4rem; margin-top: 30px; margin-bottom: 20px; }
    h3 { font-size: 1.1rem; margin-bottom: 10px; }
    p { margin-bottom: 16px; line-height: 1.6; }

    .lang { display: none; }
    .lang.active { display: block; }

    .topic-link { color: #0070f3; text-decoration: none; }
    .topic-link:hover { text-decoration: underline; }

    /* NUEVO DISEÑO DE CARDS */
    .topics-container {
      display: grid;
      grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
      gap: 20px;
      margin-top: 20px;
    }

    .topic-card {
      background: #f9f9f9;
      padding: 20px;
      border-radius: 12px;
      box-shadow: 0 2px 8px rgba(0,0,0,0.08);
      transition: transform 0.2s, box-shadow 0.2s;
      display: flex;
      flex-direction: column;
      justify-content: space-between;
    }

    .topic-card:hover {
      transform: translateY(-5px);
      box-shadow: 0 6px 15px rgba(0,0,0,0.12);
    }

    .topic-card h3 {
      margin-bottom: 10px;
      font-size: 1.2rem;
      color: #111;
    }

    .topic-card p {
      flex: 1;
      font-size: 0.95rem;
      color: #333;
    }

    .topic-card a {
      margin-top: 10px;
      font-weight: 500;
      color: #0070f3;
      text-decoration: none;
      align-self: flex-start;
    }
    .topic-card a:hover { text-decoration: underline; }