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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
    padding: 20px;
}

.container {
    max-width: 900px;
    margin: 0 auto;
}

header {
    text-align: center;
    margin-bottom: 30px;
    color: white;
}

header h1 {
    font-size: 2.5rem;
    margin-bottom: 20px;
    text-shadow: 2px 2px 4px rgba(0,0,0,0.3);
}

.progress-bar {
    width: 100%;
    height: 8px;
    background-color: rgba(255,255,255,0.3);
    border-radius: 4px;
    margin-bottom: 15px;
    overflow: hidden;
}

.progress-fill {
    height: 100%;
    background-color: #4CAF50;
    width: 0%;
    transition: width 0.3s ease;
}

.score-info {
    display: flex;
    justify-content: space-between;
    font-size: 1.1rem;
    font-weight: 500;
}

.flashcard-container {
    margin-bottom: 30px;
}

.card {
    background: white;
    border-radius: 15px;
    box-shadow: 0 10px 30px rgba(0,0,0,0.2);
    margin-bottom: 20px;
    overflow: hidden;
    transition: transform 0.3s ease, box-shadow 0.3s ease;
}

.card:hover {
    transform: translateY(-5px);
    box-shadow: 0 15px 40px rgba(0,0,0,0.3);
}

.card-header {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    padding: 20px;
    text-align: center;
}

.card-header h2 {
    font-size: 1.5rem;
    margin-bottom: 5px;
}

.domain-label {
    font-size: 0.9rem;
    opacity: 0.9;
    font-weight: normal;
}

.card-content {
    padding: 30px;
}

#questionText {
    font-size: 1.2rem;
    line-height: 1.6;
    margin-bottom: 25px;
    color: #333;
}

.choices {
    margin-bottom: 25px;
}

.choice {
    background: #f8f9fa;
    border: 2px solid #e9ecef;
    border-radius: 8px;
    padding: 15px 20px;
    margin-bottom: 10px;
    cursor: pointer;
    transition: all 0.3s ease;
    display: flex;
    align-items: center;
}

.choice:hover {
    background: #e9ecef;
    border-color: #667eea;
}

.choice.selected {
    background: #e3f2fd;
    border-color: #2196F3;
    color: #1976D2;
}

.choice.correct {
    background: #e8f5e8;
    border-color: #4CAF50;
    color: #2e7d32;
}

.choice.incorrect {
    background: #ffebee;
    border-color: #f44336;
    color: #c62828;
}

.choice-letter {
    font-weight: bold;
    margin-right: 15px;
    width: 25px;
    height: 25px;
    background: #667eea;
    color: white;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.9rem;
}

.choice.correct .choice-letter {
    background: #4CAF50;
}

.choice.incorrect .choice-letter {
    background: #f44336;
}

.card-actions {
    text-align: center;
}

.btn {
    background: #667eea;
    color: white;
    border: none;
    border-radius: 8px;
    padding: 12px 25px;
    font-size: 1rem;
    cursor: pointer;
    transition: all 0.3s ease;
    margin: 0 10px;
}

.btn:hover {
    background: #5a6fd8;
    transform: translateY(-2px);
}

.btn-secondary {
    background: #28a745;
}

.btn-secondary:hover {
    background: #218838;
}

.btn-outline {
    background: transparent;
    border: 2px solid white;
    color: white;
}

.btn-outline:hover {
    background: white;
    color: #667eea;
}

.answer-card {
    border-left: 5px solid #4CAF50;
}

.correct-answer {
    font-size: 1.3rem;
    font-weight: bold;
    color: #2e7d32;
    margin-bottom: 15px;
}

.explanation {
    font-size: 1.1rem;
    line-height: 1.6;
    color: #555;
    background: #f8f9fa;
    padding: 20px;
    border-radius: 8px;
    border-left: 4px solid #4CAF50;
}

.controls {
    display: flex;
    justify-content: center;
    gap: 15px;
    margin-bottom: 30px;
}

footer {
    text-align: center;
    color: rgba(255,255,255,0.8);
    font-size: 0.9rem;
}

.fade-in {
    animation: fadeIn 0.5s ease-in;
}

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

/* Responsive Design */
@media (max-width: 768px) {
    .container {
        padding: 10px;
    }
    
    header h1 {
        font-size: 2rem;
    }
    
    .score-info {
        flex-direction: column;
        gap: 5px;
    }
    
    .card-content {
        padding: 20px;
    }
    
    #questionText {
        font-size: 1.1rem;
    }
    
    .choice {
        padding: 12px 15px;
    }
    
    .controls {
        flex-direction: column;
        align-items: center;
    }
    
    .btn {
        width: 100%;
        max-width: 200px;
        margin: 5px 0;
    }
}