:root {
        --primary: #4f46e5;
        --primary-light: #eef2ff;
        --success: #16a34a;
        --danger: #dc2626;
        --text: #1e293b;
        --muted: #64748b;
        --border: #e2e8f0;
        --bg: #f1f5f9;
      }

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

      body {
        font-family: Arial, Helvetica, sans-serif;
        background: var(--bg);
        color: var(--text);
        line-height: 1.6;
      }

      button {
        font: inherit;
        cursor: pointer;
        border: none;
      }

      button:disabled {
        cursor: not-allowed;
        opacity: 0.45;
      }

      .header {
        background: white;
        border-bottom: 1px solid var(--border);
        padding: 16px 5%;
        display: flex;
        align-items: center;
        justify-content: space-between;
        gap: 16px;
      }

      .brand {
        font-size: 21px;
        font-weight: 800;
        color: var(--primary);
      }

      .header-subtitle {
        color: var(--muted);
        font-size: 13px;
      }

      .container {
        max-width: 1100px;
        margin: 30px auto;
        padding: 0 18px;
      }

      .exam-info {
        display: grid;
        grid-template-columns: minmax(0, 1.35fr) minmax(130px, 0.7fr) minmax(
            160px,
            0.85fr
          );
        gap: 14px;
        margin-bottom: 22px;
      }

      .info-card {
        background: white;
        padding: 18px;
        border-radius: 12px;
        border: 1px solid var(--border);
        min-width: 0;
        overflow: hidden;
      }

      /* Tên đề thi dài vẫn nằm gọn trong thẻ */
      .exam-name {
        font-size: clamp(15px, 1.5vw, 18px);
        line-height: 1.4;
        font-weight: 700;
        overflow-wrap: anywhere;
        display: -webkit-box;
        -webkit-box-orient: vertical;
        -webkit-line-clamp: 2;
        line-clamp: 2;
        overflow: hidden;
      }

      .exam-info .info-value {
        min-width: 0;
        overflow-wrap: anywhere;
      }

      .info-label {
        color: var(--muted);
        font-size: 13px;
        margin-bottom: 5px;
      }

      .info-value {
        font-size: 21px;
        font-weight: 700;
      }

      .timer {
        color: var(--danger);
      }

      .progress-wrapper {
        background: #e2e8f0;
        height: 8px;
        border-radius: 10px;
        overflow: hidden;
        margin-top: 10px;
      }

      .progress-bar {
        width: 0;
        height: 100%;
        background: var(--primary);
        transition: width 0.3s;
      }

      .exam-layout {
        display: grid;
        grid-template-columns: minmax(0, 1fr) 270px;
        gap: 22px;
        align-items: start;
      }

      .question-card,
      .sidebar,
      .result-card {
        background: white;
        border: 1px solid var(--border);
        border-radius: 14px;
        padding: 26px;
        box-shadow: 0 4px 16px rgba(15, 23, 42, 0.03);
      }

      .question-meta {
        display: flex;
        justify-content: space-between;
        align-items: center;
        gap: 10px;
        margin-bottom: 18px;
      }

      .question-badge {
        background: var(--primary-light);
        color: var(--primary);
        padding: 5px 12px;
        border-radius: 20px;
        font-size: 16px;
        font-weight: 700;
      }

      .question-title {
        font-size: 20px;
        line-height: 1.6;
        margin-bottom: 24px;
        white-space: pre-line;
      }

      .options {
        display: flex;
        flex-direction: column;
        gap: 12px;
      }

      .option {
        width: 100%;
        text-align: left;
        padding: 15px;
        border: 1.5px solid var(--border);
        border-radius: 10px;
        display: flex;
        gap: 13px;
        align-items: flex-start;
        background: white;
        transition: 0.2s;
        color: #1e293b;
      }

      .option:not(:disabled):hover {
        border-color: var(--primary);
        background: #fafaff;
      }

      .option.selected {
        border-color: var(--primary);
        color: #1e293b;
        background: var(--primary-light);
      }

      .option.correct {
        border-color: var(--success);
        background: #f0fdf4;
      }

      .option.wrong {
        border-color: var(--danger);
        background: #fef2f2;
      }

      .option-letter {
        flex-shrink: 0;
        width: 30px;
        height: 30px;
        border-radius: 8px;
        display: grid;
        place-items: center;
        background: #f1f5f9;
        font-weight: 700;
      }

      .option.selected .option-letter {
        color: white;
        background: var(--primary);
      }

      .option.correct .option-letter {
        color: white;
        background: var(--success);
      }

      .option.wrong .option-letter {
        color: white;
        background: var(--danger);
      }

      .explanation {
        display: none;
        margin-top: 20px;
        padding: 15px;
        background: #f8fafc;
        border-radius: 10px;
        border-left: 4px solid var(--primary);
      }

      .explanation.show {
        display: block;
      }

      .navigation {
        display: flex;
        justify-content: space-between;
        gap: 12px;
        margin-top: 28px;
      }

      .btn {
        padding: 11px 18px;
        border-radius: 9px;
        font-weight: 700;
        transition: 0.2s;
      }

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

      .btn-primary:hover {
        background: #4338ca;
      }

      .btn-secondary {
        background: #f1f5f9;
        color: var(--text);
      }

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

      .sidebar h3 {
        font-size: 17px;
        margin-bottom: 5px;
      }

      .sidebar-desc {
        font-size: 13px;
        color: var(--muted);
        margin-bottom: 18px;
      }

      .question-grid {
        display: grid;
        grid-template-columns: repeat(5, 1fr);
        gap: 8px;
      }

      .question-number {
        aspect-ratio: 1;
        border-radius: 8px;
        background: #f1f5f9;
        color: var(--text);
        font-weight: 700;
        border: 1px solid transparent;
      }

      .question-number.answered {
        background: #dcfce7;
        color: #166534;
      }

      .question-number.current {
        border: 2px solid var(--primary);
        color: var(--primary);
      }

      .question-number.correct {
        background: #dcfce7;
        color: #166534;
      }

      .question-number.wrong {
        background: #fee2e2;
        color: #991b1b;
      }

      .legend {
        margin-top: 18px;
        font-size: 12px;
        color: var(--muted);
        display: grid;
        gap: 7px;
      }

      .legend span {
        display: inline-flex;
        align-items: center;
        gap: 8px;
      }

      .dot {
        display: inline-block;
        width: 12px;
        height: 12px;
        border-radius: 3px;
        background: #dcfce7;
      }

      .dot-gray {
        background: #f1f5f9;
      }

      .submit-sidebar {
        width: 100%;
        margin-top: 22px;
      }

      .result-card {
        display: none;
        margin-top: 24px;
        text-align: center;
      }

      .result-card.show {
        display: block;
      }

      .result-score {
        font-size: 48px;
        font-weight: 800;
        color: var(--primary);
        margin: 10px 0;
      }

      .result-details {
        color: var(--muted);
        margin-bottom: 20px;
      }

      .result-summary {
        display: flex;
        justify-content: center;
        gap: 25px;
        flex-wrap: wrap;
        margin: 20px 0;
      }

      .result-summary strong {
        display: block;
        font-size: 23px;
      }

      .result-summary .green {
        color: var(--success);
      }

      .result-summary .red {
        color: var(--danger);
      }

      .footer {
        text-align: center;
        padding: 25px;
        color: var(--muted);
        font-size: 13px;
      }

      .hidden {
        display: none !important;
      }

      @media (max-width: 800px) {
        .exam-layout {
          grid-template-columns: 1fr;
        }

        .sidebar {
          order: -1;
        }

        .question-grid {
          grid-template-columns: repeat(10, 1fr);
        }

        .exam-info {
          gap: 8px;
          grid-template-columns: minmax(0, 1.2fr) minmax(120px, 0.8fr);
        }

        .exam-info .info-card:first-child {
          grid-column: 1 / -1;
        }

        .info-card {
          padding: 14px;
        }

        .info-value {
          font-size: 17px;
        }

        .exam-name {
          font-size: 16px;
          -webkit-line-clamp: 3;
          line-clamp: 3;
        }
      }

      @media (max-width: 480px) {
        .header {
          padding: 12px 16px;
        }

        .brand {
          font-size: 17px;
        }

        .header-subtitle {
          display: none;
        }

        .container {
          margin-top: 18px;
          padding: 0 12px;
        }

        .question-card,
        .sidebar,
        .result-card {
          padding: 17px;
        }

        .question-title {
          font-size: 17px;
        }

        .question-grid {
          grid-template-columns: repeat(5, 1fr);
        }

        .navigation .btn {
          padding: 10px 12px;
          font-size: 13px;
        }
      }
      .question-number.unanswered {
        background: #fef3c7;
        color: #92400e;
      }

      .result-time {
        display: flex;
        justify-content: center;
        align-items: center;
        gap: 8px;
        margin: -10px 0 20px;
        color: var(--muted);
        font-size: 15px;
      }

      .result-time strong {
        color: var(--primary);
        font-size: 17px;
        font-weight: 700;
      }
      #resultCard {
        scroll-margin-top: 20px;
      }