.hidden {
    display: none !important;
}

:root {
    --primary-color: #3498db;
    --secondary-color: #2c3e50;
    --success-color: #2ecc71;
    --danger-color: #e74c3c;
    --warning-color: #f39c12;
    --info-color: #3498db;
    --light-color: #ecf0f1;
    --dark-color: #34495e;
    --shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
    --border-radius: 10px;
    --transition: all 0.3s ease;
    --gap: 20px;
}

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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    line-height: 1.6;
    color: #333;
    background: linear-gradient(135deg, #f5f7fa 0%, #e4edf5 100%);
    min-height: 100vh;
    padding: 15px;
}

.container {
    max-width: 1400px;
    margin: 0 auto;
}

header {
    text-align: center;
    margin-bottom: 20px;
    padding: 15px;
    background: linear-gradient(120deg, var(--secondary-color), var(--dark-color));
    color: white;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    transition: var(--transition);
}

header:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 12px rgba(0, 0, 0, 0.15);
}

h1 {
    font-size: 1.8rem;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 10px;
}

.main-content {
    display: flex;
    gap: var(--gap);
    margin-bottom: 20px;
}

.sidebar {
    width: 280px;
    background-color: white;
    padding: 20px;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    height: fit-content;
    position: sticky;
    top: 15px;
    transition: var(--transition);
    flex-shrink: 0;
}

.sidebar:hover {
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.15);
}

.sidebar-header {
    margin-bottom: 15px;
    padding-bottom: 10px;
    border-bottom: 2px solid var(--light-color);
}

.sidebar h3 {
    color: var(--secondary-color);
    font-size: 1.2rem;
    display: flex;
    align-items: center;
    gap: 8px;
}

.chapter-list {
    list-style: none;
    margin-bottom: 20px;
    padding-left: 5px;
}

.chapter-list li {
    padding: 10px 15px;
    margin-bottom: 8px;
    background-color: var(--light-color);
    border-radius: 6px;
    cursor: pointer;
    transition: var(--transition);
    display: flex;
    align-items: center;
    gap: 10px;
    font-size: 0.95rem;
    font-weight: 500;
}

.chapter-list li:hover {
    background-color: #d6eaf8;
    transform: translateX(3px);
}

.chapter-list li.active {
    background: linear-gradient(120deg, var(--primary-color), #1a5276);
    color: white;
    box-shadow: 0 3px 6px rgba(52, 152, 219, 0.3);
}

.progress-section {
    margin-bottom: 20px;
}

.progress-bar {
    height: 10px;
    background-color: #e0e6ed;
    border-radius: 5px;
    margin: 12px 0;
    overflow: hidden;
    box-shadow: inset 0 1px 2px rgba(0,0,0,0.1);
}

.progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--primary-color), var(--success-color));
    border-radius: 5px;
    transition: width 0.5s ease;
}

.progress-stats {
    text-align: center;
    font-weight: bold;
    color: var(--secondary-color);
    margin-top: 5px;
    font-size: 1rem;
}

.tips {
    background-color: #f8f9fa;
    padding: 15px;
    border-radius: 6px;
    border-left: 3px solid var(--primary-color);
    font-size: 0.95rem;
}

.tips ul {
    margin-top: 8px;
    padding-left: 18px;
}

.tips li {
    margin-bottom: 6px;
    line-height: 1.5;
}

.content-area {
    flex: 1;
    min-width: 0;
}

.test-selection {
    background: white;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    padding: 30px;
    text-align: center;
    transition: var(--transition);
    height: 100%;
}

.test-selection:hover {
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.12);
}

.test-selection h2 {
    color: var(--secondary-color);
    margin-bottom: 15px;
    font-size: 1.8rem;
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 12px;
}

.test-selection p {
    font-size: 1.05rem;
    color: #555;
    margin-bottom: 25px;
    line-height: 1.6;
}

.test-buttons {
    display: flex;
    justify-content: center;
    gap: 15px;
    flex-wrap: wrap;
    margin-bottom: 25px;
}

.test-btn {
    padding: 12px 25px;
    font-size: 1.05rem;
    background: linear-gradient(120deg, var(--primary-color), #1a5276);
    color: white;
    border: none;
    border-radius: 50px;
    cursor: pointer;
    transition: var(--transition);
    font-weight: 600;
    box-shadow: 0 3px 8px rgba(52, 152, 219, 0.4);
    display: flex;
    align-items: center;
    gap: 6px;
}

.test-btn:hover {
    transform: translateY(-2px) scale(1.03);
    box-shadow: 0 5px 12px rgba(52, 152, 219, 0.6);
}

.test-info {
    margin-top: 20px;
    padding: 12px;
    background-color: #e8f4fd;
    border-radius: 6px;
    color: var(--dark-color);
    font-size: 0.95rem;
}

.test-info i {
    color: var(--primary-color);
    margin-right: 6px;
}

.test-content {
    background: white;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    padding: 25px;
    display: none;
    transition: var(--transition);
}

.test-content h3 {
    color: var(--secondary-color);
    margin-bottom: 15px;
    padding-bottom: 8px;
    border-bottom: 2px solid var(--light-color);
    font-size: 1.4rem;
    display: flex;
    align-items: center;
    gap: 8px;
}

.directions-section {
    background-color: #f8f9fa;
    padding: 20px;
    border-radius: 6px;
    margin-bottom: 20px;
    border-left: 3px solid var(--primary-color);
}

.directions-text {
    line-height: 1.7;
    font-size: 1.05rem;
    color: #444;
}

.audio-section {
    margin-bottom: 25px;
    background-color: #f8f9fa;
    padding: 15px;
    border-radius: 6px;
}

.audio-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 12px;
    font-size: 1.1rem;
}

.audio-info {
    color: var(--dark-color);
    font-size: 0.9rem;
}

.filename {
    font-weight: bold;
    color: var(--primary-color);
}

.audio-player {
    background: white;
    padding: 15px;
    border-radius: 6px;
    box-shadow: 0 2px 6px rgba(0,0,0,0.08);
}

#audio-player {
    width: 100%;
    margin-bottom: 10px;
    height: 40px;
}

.audio-controls {
    display: flex;
    gap: 12px;
    justify-content: center;
    margin-top: 8px;
    margin-bottom: 15px;
}

.control-btn {
    padding: 8px 18px;
    background: linear-gradient(120deg, var(--primary-color), #1a5276);
    color: white;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    transition: var(--transition);
    font-weight: 500;
    font-size: 0.95rem;
    display: flex;
    align-items: center;
    gap: 6px;
}

.control-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 3px 7px rgba(52, 152, 219, 0.4);
}

.toggle-btn {
    padding: 8px 18px;
    background: linear-gradient(120deg, var(--info-color), #1a5276);
    color: white;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    transition: var(--transition);
    font-weight: 500;
    font-size: 0.95rem;
    display: flex;
    align-items: center;
    gap: 6px;
    margin: 0 auto;
}

.toggle-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 3px 7px rgba(52, 152, 219, 0.4);
}

.transcript-section {
    margin-top: 15px;
    padding: 15px;
    background-color: #e8f4fd;
    border-radius: 6px;
    border-left: 3px solid var(--primary-color);
}

.transcript-section h4 {
    color: var(--secondary-color);
    margin-bottom: 8px;
    font-size: 1.1rem;
}

.transcript-content, .translation-content {
    line-height: 1.8;
    font-size: 1rem;
    margin-bottom: 10px;
}

.transcript-content {
    color: #2c3e50;
}

.translation-content {
    font-weight: 500
}

.original-text, .translation-text {
    margin-bottom: 15px;
}

.questions-section {
    margin-bottom: 25px;
}

.questions-container {
    background-color: #f9fafc;
    padding: 20px;
    border-radius: 8px;
}

.question-group {
    margin-bottom: 25px;
}

.section-title {
    font-weight: bold;
    color: var(--secondary-color);
    margin-bottom: 15px;
    font-size: 1.2rem;
    padding-bottom: 8px;
    border-bottom: 1px solid #eaeaea;
}

.question {
    margin-bottom: 22px;
    padding-bottom: 15px;
    border-bottom: 1px dashed #eaeaea;
    position: relative;
}

.question:last-child {
    margin-bottom: 0;
    padding-bottom: 0;
    border-bottom: none;
}

.question-title {
    font-weight: 600;
    margin-bottom: 12px;
    color: var(--secondary-color);
    font-size: 1.05rem;
    line-height: 1.5;
}

.questions-hidden .question-title {
    display: none !important;
}

.question-number {
    color: var(--primary-color);
    font-weight: bold;
    margin-right: 5px;
}

.options {
    list-style: none;
    padding-left: 10px;
    margin-top: 5px;
}

.option {
    margin-bottom: 8px;
    padding: 10px 15px 10px 35px;
    border: 1px solid #ddd;
    border-radius: 6px;
    cursor: pointer;
    transition: var(--transition);
    font-size: 0.98rem;
    position: relative;
}

.option::before {
    content: "";
    position: absolute;
    left: 10px;
    top: 50%;
    transform: translateY(-50%);
    width: 16px;
    height: 16px;
    border: 2px solid #888;
    border-radius: 50%;
}

.option:hover {
    background-color: #e3f2fd;
    border-color: #bbdefb;
}

.option.selected {
    background-color: #e3f2fd;
    border-color: var(--primary-color);
}

.option.selected::before {
    background-color: var(--primary-color);
    border-color: var(--primary-color);
}

.option.correct {
    background-color: #e8f5e9;
    border-color: #81c784;
    animation: highlightCorrect 0.5s ease;
}

.option.correct::before {
    background-color: #4caf50;
    border-color: #4caf50;
}

.option.incorrect {
    background-color: #ffebee;
    border-color: #ef9a9a;
    animation: highlightIncorrect 0.5s ease;
}

.option.incorrect::before {
    background-color: #f44336;
    border-color: #f44336;
}

.option-letter {
    position: absolute;
    left: 12px;
    top: 50%;
    transform: translateY(-50%);
    font-weight: bold;
    color: #555;
}

@keyframes highlightCorrect {
    0% { box-shadow: 0 0 0 0 rgba(76, 175, 80, 0.3); }
    70% { box-shadow: 0 0 0 10px rgba(76, 175, 80, 0.3); }
    100% { box-shadow: 0 0 0 0 rgba(76, 175, 80, 0.3); }
}

@keyframes highlightIncorrect {
    0% { box-shadow: 0 0 0 0 rgba(244, 67, 54, 0.3); }
    70% { box-shadow: 0 0 0 10px rgba(244, 67, 54, 0.3); }
    100% { box-shadow: 0 0 0 0 rgba(244, 67, 54, 0.3); }
}

.explanation-section {
    margin-top: 15px;
    padding: 15px;
    background-color: #f8f9fa;
    border-radius: 6px;
    border-left: 3px solid var(--info-color);
    display: none;
}

.explanation-section.show {
    display: block;
    animation: fadeIn 0.5s ease;
}

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

.correct-answer {
    font-weight: bold;
    color: #4caf50;
    margin-right: 15px;
}

.user-answer {
    font-weight: bold;
    color: #f44336;
    margin-right: 15px;
}

.explanation-text {
    margin-top: 8px;
    line-height: 1.6;
    color: #555;
}

.navigation-section {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding-top: 15px;
    border-top: 2px solid var(--light-color);
    margin-top: 15px;
}

.nav-buttons {
    display: flex;
    gap: 12px;
    flex-wrap: wrap;
    align-items: center;
}

#prev-passage-btn, #next-passage-btn, #prev-section-btn, #next-section-btn {
    padding: 8px 20px;
    background-color: var(--dark-color);
    color: white;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    font-size: 0.95rem;
    transition: var(--transition);
    display: flex;
    align-items: center;
    gap: 6px;
}

.prev-passage-btn:hover, #next-passage-btn:hover, #prev-section-btn:hover, #next-section-btn:hover {
    background-color: #233040;
    transform: translateY(-2px);
}

#prev-passage-btn:disabled, #next-passage-btn:disabled, #prev-section-btn:disabled, #next-section-btn:disabled {
    background-color: #95a5a6;
    cursor: not-allowed;
    transform: none;
}

#prev-passage-btn:disabled:hover, #next-passage-btn:disabled:hover, #prev-section-btn:disabled:hover, #next-section-btn:disabled:hover {
    background-color: #95a5a6;
}

.submit-btn {
    padding: 8px 22px;
    background: linear-gradient(120deg, var(--danger-color), #c0392b);
    color: white;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    font-size: 1.05rem;
    font-weight: 600;
    transition: var(--transition);
    display: flex;
    align-items: center;
    gap: 6px;
}

.submit-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 3px 8px rgba(231, 76, 60, 0.4);
}

.action-btn {
    padding: 8px 18px;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    font-size: 0.95rem;
    transition: var(--transition);
    display: flex;
    align-items: center;
    gap: 6px;
}

.action-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 3px 7px rgba(0,0,0,0.1);
}

.action-btn.tertiary {
    background-color: #f1f3f5;
    color: #707070;
    border: 1px solid #d0d0d0;
}

.section-info {
    background-color: var(--primary-color);
    color: white;
    padding: 5px 12px;
    border-radius: 15px;
    font-weight: bold;
    font-size: 1rem;
    margin-top: 10px;
    margin-left: auto;
}

footer {
    text-align: center;
    padding: 20px;
    color: var(--dark-color);
    font-size: 1rem;
    margin-top: 15px;
    border-top: 1px solid #e0e6ed;
}

/* 响应式设计 */
@media (max-width: 992px) {
    .main-content {
        flex-direction: column;
    }
    
    .sidebar {
        width: 100%;
        position: static;
        margin-bottom: 20px;
    }
}

@media (max-width: 768px) {
    .test-buttons {
        flex-direction: column;
        align-items: center;
    }
    
    .test-btn {
        width: 85%;
        margin-bottom: 10px;
    }
    
    .nav-buttons {
        flex-direction: row;
        gap: 10px;
        width: 100%;
        justify-content: center;
        flex-wrap: wrap;
        margin-bottom: 10px;
    }
    
    #prev-passage-btn, #next-passage-btn, #prev-section-btn, #next-section-btn, .submit-btn, .action-btn {
        width: auto;
        justify-content: center;
        font-size: 0.85rem;
        padding: 6px 15px;
    }
    
    .section-info {
        margin-top: 15px;
        margin-left: 0;
        font-size: 0.9rem;
    }
    
    .control-btn, .toggle-btn {
        padding: 8px 15px;
        font-size: 0.9rem;
    }
    
    .question {
        margin-bottom: 18px;
    }
}

@media (max-width: 480px) {
    .container {
        padding: 10px;
    }
    
    header h1 {
        font-size: 1.6rem;
    }
    
    .test-selection {
        padding: 20px 15px;
    }
    
    .test-btn {
        width: 95%;
        padding: 10px 15px;
        font-size: 1rem;
    }
    
    .sidebar {
        padding: 15px 10px;
    }
    
    .chapter-list li {
        padding: 8px 12px;
        font-size: 0.9rem;
    }
    
    .test-content {
        padding: 20px 15px;
    }
    
    .questions-container {
        padding: 15px;
    }
    
    .audio-player {
        padding: 12px;
    }
    
    .question-title {
        font-size: 1rem;
    }
    
    .option {
        font-size: 0.95rem;
        padding-left: 30px;
    }
    
    .transcript-section {
        padding: 10px;
    }
    
    .transcript-content, .translation-content {
        font-size: 0.95rem;
        line-height: 1.7;
    }
    
    .nav-buttons {
        flex-direction: column;
        align-items: stretch;
    }
    
    #prev-passage-btn, #next-passage-btn, #prev-section-btn, #next-section-btn {
        width: 100%;
        margin-bottom: 8px;
    }
}