:root {
        --primary-color: rgba(1, 1, 1, 0.9);
        --secondary-color: #ff8c42;
        --accent-color: #ff6600;
        --light-color: #ffd8b5;
        --text-color: #333;
        --white: #ffffff;
        --black: #000000;
        --orange-gradient: linear-gradient(
          115deg,
          #ff6701,
          #ff9900,
          #fd640b,
          #ff8851,
          #ff9810,
          #ff7951
        );
        --success-color: #4caf50;
        --error-color: #f44336;
        --orange-bg: #b9b8b7;

        /* Variables adicionales para el ejercicio */
        --bg: var(--orange-bg);
        --card: var(--white);
        --border: #ffc299;
        --primary: var(--secondary-color);
        --success: var(--success-color);
        --danger: var(--error-color);
        --dim: #b36b3c;
        --yellow: #fff5e6;
        --yellow-border: #ffb37c;
        --light: #fffaf5;
      }

      * {
        font-family: "Poppins", sans-serif;
        box-sizing: border-box;
        margin: 0;
        padding: 0;
      }

      body {
        min-height: 100vh;
        background-color: var(--orange-bg);
        color: var(--text-color);
        padding-top: 80px; /* espacio para el header fijo */
      }

      /* Header Styles */
      .header {
        position: fixed;
        top: 0;
        left: 0;
        right: 0;
        background-color: rgba(1, 1, 1, 0.9);
        padding: 0 10%;
        display: flex;
        align-items: center;
        justify-content: space-between;
        z-index: 1000;
        box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
        border-bottom: 2px solid var(--secondary-color);
        transition: all 0.3s ease;
      }

      .header:hover {
        box-shadow: 0 6px 16px rgba(0, 0, 0, 0.4);
      }

      .logo {
        font-size: 28px;
        font-weight: 700;
        color: var(--white);
        text-shadow: 1px 1px 2px rgba(0, 0, 0, 0.3);
        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-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: var(--secondary-color);
        transform: translateY(-2px);
        color: var(--black);
      }

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

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

      /* Main Container */
      .main-container {
        max-width: 1200px;
        margin: 0 auto;
        padding: 20px;
      }

      /* Title */
      h1 {
        text-align: center;
        color: var(--black);
        margin-bottom: 30px;
        font-size: 2.5rem;
        font-weight: 700;
        text-shadow: 1px 1px 3px rgba(0, 0, 0, 0.1);
        position: relative;
        padding-bottom: 15px;
      }

      h1::after {
        content: "";
        position: absolute;
        bottom: 0;
        left: 50%;
        transform: translateX(-50%);
        width: 120px;
        height: 4px;
        background: var(--orange-gradient);
        border-radius: 4px;
      }

      /* Tag and subtitle (del ejercicio original) */
      .tag {
        display: inline-block;
        font-size: 0.65rem;
        font-weight: 700;
        letter-spacing: 2px;
        text-transform: uppercase;
        color: var(--dim);
        border: 1.5px solid var(--border);
        padding: 3px 14px;
        border-radius: 50px;
        margin-bottom: 0.6rem;
        background: var(--white);
      }

      .subtitle {
        color: var(--dim);
        font-size: 0.82rem;
        margin-top: 0.3rem;
      }

      /* Exercise header (reemplaza al antiguo header) */
      .exercise-header {
        text-align: center;
        margin-bottom: 2rem;
      }

      /* Card */
      .card {
        max-width: 760px;
        margin: 0 auto;
        background: var(--card);
        border: 1px solid var(--border);
        border-radius: 16px;
        overflow: hidden;
        box-shadow: 0 4px 24px rgba(255, 102, 0, 0.1);
      }

      .card-header {
        background: var(--light);
        padding: 0.9rem 1.8rem;
        font-size: 0.72rem;
        font-weight: 700;
        color: var(--dim);
        letter-spacing: 2px;
        text-transform: uppercase;
        border-bottom: 1px solid var(--border);
      }

      .instr-box {
        background: var(--yellow);
        border: 1.5px solid var(--yellow-border);
        border-radius: 10px;
        padding: 0.75rem 1.2rem;
        margin: 1.2rem 1.5rem 0.5rem;
        font-size: 0.82rem;
        color: #a35100;
        font-weight: 600;
        line-height: 1.5;
      }

      /* Sentences */
      .sentences {
        padding: 1rem 1.5rem 1.5rem;
      }

      .s-item {
        display: flex;
        align-items: baseline;
        gap: 0.5rem;
        padding: 0.55rem 0.7rem;
        border-radius: 8px;
        margin-bottom: 0.3rem;
        border: 1.5px solid transparent;
        transition: background 0.15s;
        flex-wrap: wrap;
        line-height: 1.9;
      }

      .s-item:hover {
        background: #ffefe2;
      }
      .s-item.correct {
        background: #e6f4ea;
        border-color: #b8e0c0;
      }
      .s-item.wrong {
        background: #ffe6e6;
        border-color: #ffb3b3;
      }

      .s-num {
        font-size: 0.72rem;
        font-weight: 700;
        color: var(--dim);
        min-width: 22px;
        flex-shrink: 0;
      }

      .s-text {
        font-size: 0.88rem;
        font-weight: 600;
        color: var(--text-color);
        display: flex;
        align-items: baseline;
        flex-wrap: wrap;
        gap: 0.3rem;
        flex: 1;
        line-height: 1.9;
      }

      .verb-hint {
        font-size: 0.72rem;
        color: var(--secondary-color);
        font-weight: 700;
        background: #ffeed9;
        border-radius: 4px;
        padding: 1px 6px;
        flex-shrink: 0;
      }

      .blank-wrap {
        display: inline-flex;
        align-items: baseline;
      }

      input.blank {
        border: none;
        border-bottom: 2px solid var(--secondary-color);
        background: transparent;
        font-family: "Poppins", sans-serif;
        font-size: 0.86rem;
        font-weight: 600;
        color: var(--secondary-color);
        width: 150px;
        outline: none;
        padding: 0 4px 1px;
        transition: border-color 0.2s;
        text-align: center;
      }

      input.blank:focus {
        border-color: var(--accent-color);
      }
      input.blank.correct {
        border-color: var(--success);
        color: var(--success);
      }
      input.blank.wrong {
        border-color: var(--danger);
        color: var(--danger);
      }
      input.blank.revealed {
        border-color: var(--dim);
        color: var(--dim);
        font-style: italic;
      }

      .feedback-icon {
        font-size: 0.8rem;
        margin-left: 4px;
      }

      /* Bottom bar */
      .bottom-bar {
        padding: 0.9rem 1.8rem;
        border-top: 1px solid var(--border);
        display: flex;
        align-items: center;
        justify-content: space-between;
        flex-wrap: wrap;
        gap: 0.6rem;
        background: var(--light);
      }

      .score-txt {
        font-size: 0.85rem;
        font-weight: 700;
        color: var(--dim);
      }

      .score-txt span {
        color: var(--secondary-color);
        font-size: 1.1rem;
      }

      .btn {
        border: none;
        border-radius: 50px;
        padding: 0.5rem 1.3rem;
        font-family: "Poppins", sans-serif;
        font-size: 0.8rem;
        font-weight: 700;
        cursor: pointer;
        transition: all 0.18s;
      }

      .btn-outline {
        background: transparent;
        border: 1.5px solid var(--border);
        color: var(--dim);
      }

      .btn-outline:hover {
        border-color: var(--secondary-color);
        color: var(--secondary-color);
        background: #fff1e6;
      }

      .btn-fill {
        background: var(--secondary-color);
        color: white;
      }

      .btn-fill:hover {
        background: var(--accent-color);
        transform: translateY(-1px);
      }

      .result-banner {
        display: none;
        margin: 0 1.5rem 1rem;
        padding: 0.8rem 1.2rem;
        border-radius: 10px;
        text-align: center;
        font-weight: 700;
        font-size: 0.88rem;
      }

      .result-banner.show {
        display: block;
      }
      .result-banner.good {
        background: #e6f4ea;
        border: 1.5px solid #b8e0c0;
        color: var(--success);
      }
      .result-banner.ok {
        background: var(--yellow);
        border: 1.5px solid var(--yellow-border);
        color: #a35100;
      }

      /* Media Queries para header responsive */
      @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;
          box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
        }

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

        .header .navigation ul li a {
          padding: 12px 20px;
          font-size: 18px;
        }

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

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

      @media (max-width: 768px) {
        .activity-container {
          grid-template-columns: 1fr;
        }

        .exercise-card {
          padding: 20px;
        }

        .action-buttons {
          flex-direction: column;
          align-items: center;
        }

        .action-btn {
          width: 100%;
          max-width: 300px;
        }

        input.blank {
          width: 110px;
        }
        .sentences {
          padding: 0.8rem 1rem 1.2rem;
        }
      }

      @media (max-width: 480px) {
        .logo {
          font-size: 22px;
        }

        .header {
          padding: 12px 5%;
        }

        h1 {
          font-size: 1.8rem;
        }

        .score-value {
          font-size: 2rem;
        }
      }