:root {
        --primary-color: #5b6abf;
        --secondary-color: #9c64a6;
        --accent-color: #6a5acd;
        --light-color: #e6e6fa;
        --success-color: #4caf50;
        --error-color: #f44336;
        --text-color: #2c3e50;
        --white: #ffffff;
      }

      /* Estilos del Header mejorado */
      .header {
        position: fixed;
        top: 0;
        left: 0;
        right: 0;
        background: linear-gradient(
          135deg,
          var(--primary-color),
          var(--secondary-color)
        );
        padding: 0 10%;
        display: flex;
        align-items: center;
        justify-content: space-between;
        z-index: 1000;
        box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
        transition: all 0.3s ease;
      }

      .header:hover {
        box-shadow: 0 6px 16px rgba(0, 0, 0, 0.15);
      }

      .logo {
        font-size: 28px;
        font-family: "Montserrat", sans-serif;
        font-weight: 700;
        color: var(--white);
        text-shadow: 1px 1px 2px rgba(0, 0, 0, 0.2);
        letter-spacing: 1px;
      }

      .navigation ul {
        list-style: none;
        margin: 0;
        padding: 0;
      }

      .header .navigation ul li {
        float: left;
        position: relative;
      }

      .header .navigation ul li a {
        font-family: "Poppins", sans-serif;
        font-size: 16px;
        font-weight: 500;
        color: var(--white);
        text-decoration: none;
        padding: 22px 20px;
        display: block;
        transition: all 0.3s ease;
      }

      .header .navigation ul li a:hover {
        background-color: rgba(255, 255, 255, 0.15);
        transform: translateY(-2px);
      }

      .header .navigation ul li ul {
        position: absolute;
        right: 0;
        width: 220px;
        background: rgba(255, 255, 255, 0.95);
        border-radius: 0 0 8px 8px;
        box-shadow: 0 8px 16px rgba(0, 0, 0, 0.1);
        display: none;
        overflow: hidden;
      }

      .header .navigation ul li ul li a {
        color: var(--text-color);
        padding: 12px 20px;
        font-size: 14px;
      }

      .header .navigation ul li ul li a:hover {
        background-color: var(--light-color);
        color: var(--primary-color);
      }

      .header .navigation ul li:hover > ul {
        display: initial;
        animation: fadeIn 0.3s ease-out;
      }

      #toggle,
      .header label {
        display: none;
        cursor: pointer;
      }

      .menu {
        width: 28px;
        height: 28px;
        filter: brightness(0) invert(1);
      }

      @media (max-width: 950px) {
        .header label {
          display: initial;
        }

        .header {
          padding: 15px 10%;
        }

        .header .navigation {
          position: absolute;
          top: 100%;
          left: 0;
          right: 0;
          background: var(--primary-color);
          display: none;
          border-radius: 0 0 12px 12px;
        }

        .header .navigation ul li {
          width: 100%;
        }

        .header .navigation ul li a {
          padding: 12px 20px;
        }

        .header .navigation ul li ul {
          position: relative;
          width: 100%;
          left: 0;
          background: rgba(255, 255, 255, 0.1);
        }

        .header .navigation ul li ul li a {
          padding-left: 30px;
        }

        #toggle:checked ~ .navigation {
          display: block;
          animation: slideDown 0.4s ease-out;
        }
      }

      /* Estilos del cuerpo y fondo */
      body {
        font-family: "Poppins", sans-serif;
        background: linear-gradient(135deg, #e0f7fa, #d1c4e9, #b3e5fc);
        margin: 0;
        padding: 0;
        padding-top: 80px;
        min-height: 100vh;
        color: var(--text-color);
        background-size: 400% 400%;
        animation: gradientBG 15s ease infinite;
      }

      /* Animación de fondo */
      @keyframes gradientBG {
        0% {
          background-position: 0% 50%;
        }
        50% {
          background-position: 100% 50%;
        }
        100% {
          background-position: 0% 50%;
        }
      }

      /* Animaciones */
      @keyframes fadeIn {
        from {
          opacity: 0;
          transform: translateY(-10px);
        }
        to {
          opacity: 1;
          transform: translateY(0);
        }
      }

      @keyframes slideDown {
        from {
          opacity: 0;
          transform: translateY(-20px);
        }
        to {
          opacity: 1;
          transform: translateY(0);
        }
      }

      @keyframes pulse {
        0% {
          transform: scale(1);
        }
        50% {
          transform: scale(1.05);
        }
        100% {
          transform: scale(1);
        }
      }

      @keyframes bounce {
        0%,
        20%,
        50%,
        80%,
        100% {
          transform: translateY(0);
        }
        40% {
          transform: translateY(-15px);
        }
        60% {
          transform: translateY(-7px);
        }
      }
      
        body {
            font-family: Arial, sans-serif;
            line-height: 1.6;
            max-width: 800px;
            margin: 0 auto;
            padding: 20px;
        }
        h1 {
            color: #2c3e50;
            text-align: center;
        }
        .exercise {
            margin-bottom: 30px;
            padding: 20px;
            background-color: #f9f9f9;
            border-radius: 5px;
        }
        .question {
            margin-bottom: 10px;
        }
        .answer-key {
            background-color: #e8f4f8;
            padding: 15px;
            border-radius: 5px;
            margin-top: 20px;
        }
        button {
            background-color: #3498db;
            color: white;
            border: none;
            padding: 8px 15px;
            border-radius: 4px;
            cursor: pointer;
            margin-top: 10px;
        }
        button:hover {
            background-color: #2980b9;
        }
        .modal {
            display: none;
            position: fixed;
            z-index: 1;
            left: 0;
            top: 0;
            width: 100%;
            height: 100%;
            overflow: auto;
            background-color: rgba(0,0,0,0.4);
        }
        .modal-content {
            background-color: #fefefe;
            margin: 15% auto;
            padding: 20px;
            border: 1px solid #888;
            width: 80%;
            max-width: 500px;
            border-radius: 8px;
            text-align: center;
        }
        .close {
            color: #aaa;
            float: right;
            font-size: 28px;
            font-weight: bold;
            cursor: pointer;
        }
        .close:hover {
            color: black;
        }
        .score-display {
            font-size: 24px;
            margin: 20px 0;
        }
        .percentage {
            font-size: 20px;
            font-weight: bold;
            color: #2c3e50;
        }
        .congrats {
            color: #27ae60;
            font-size: 22px;
            font-weight: bold;
            margin-bottom: 15px;
            animation: pulse 1.5s infinite;
        }
        .emoji {
            font-size: 40px;
            margin-bottom: 15px;
        }
        .progress-container {
            width: 100%;
            background-color: #e0e0e0;
            border-radius: 10px;
            margin: 20px 0;
        }
        .progress-bar {
            height: 20px;
            border-radius: 10px;
            background: linear-gradient(90deg, #4CAF50, #8BC34A);
            text-align: center;
            line-height: 20px;
            color: white;
            transition: width 0.5s ease;
        }