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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
    color: #333;
    line-height: 1.6;
}

.container {
    max-width: 900px;
    margin: 0 auto;
    padding: 20px;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

.header {
    text-align: center;
    margin-bottom: 2rem;
    color: white;
}

.title {
    font-size: 2.5rem;
    font-weight: 700;
    margin-bottom: 0.5rem;
    text-shadow: 0 2px 4px rgba(0,0,0,0.3);
}

.subtitle {
    font-size: 1.1rem;
    opacity: 0.9;
    font-weight: 300;
}

.quiz-container {
    flex: 1;
    background: white;
    border-radius: 20px;
    box-shadow: 0 20px 40px rgba(0,0,0,0.1);
    overflow: hidden;
    position: relative;
}

.screen {
    display: none;
    padding: 2rem;
    min-height: 500px;
}

.screen.active {
    display: block;
}

/* Start Screen */
.start-content {
    text-align: center;
    max-width: 600px;
    margin: 0 auto;
    padding: 2rem 0;
}

.quiz-info h2 {
    font-size: 2rem;
    margin-bottom: 1rem;
    color: #2d3748;
}

.quiz-info p {
    font-size: 1.1rem;
    margin-bottom: 2rem;
    color: #4a5568;
}

.features {
    list-style: none;
    text-align: left;
    margin: 2rem 0;
    background: #f7fafc;
    padding: 1.5rem;
    border-radius: 12px;
}

.features li {
    margin: 0.8rem 0;
    font-size: 1rem;
    color: #2d3748;
    display: flex;
    align-items: center;
}

.features li::before {
    content: '✓';
    color: #48bb78;
    font-weight: bold;
    margin-right: 0.8rem;
    font-size: 1.2rem;
}

/* Buttons */
.btn {
    padding: 12px 24px;
    border: none;
    border-radius: 8px;
    font-size: 1rem;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.3s ease;
    text-decoration: none;
    display: inline-block;
    font-family: inherit;
}

.btn-primary {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
}

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 20px rgba(102, 126, 234, 0.4);
}

.btn-secondary {
    background: #e2e8f0;
    color: #4a5568;
}

.btn-secondary:hover {
    background: #cbd5e0;
    transform: translateY(-1px);
}

.btn-success {
    background: linear-gradient(135deg, #48bb78 0%, #38a169 100%);
    color: white;
}

.btn-success:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 20px rgba(72, 187, 120, 0.4);
}

.btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
    transform: none !important;
    box-shadow: none !important;
}

/* Progress Bar */
.progress-bar {
    background: #f7fafc;
    height: 60px;
    display: flex;
    align-items: center;
    justify-content: center;
    position: relative;
    margin: -2rem -2rem 2rem -2rem;
}

.progress-fill {
    position: absolute;
    left: 0;
    top: 0;
    height: 100%;
    background: linear-gradient(90deg, #667eea 0%, #764ba2 100%);
    transition: width 0.5s ease;
    width: 5%;
}

.progress-text {
    font-weight: 600;
    color: #2d3748;
    z-index: 1;
    position: relative;
}

/* Question Container */
.question-container {
    max-width: 700px;
    margin: 0 auto;
}

.question-number {
    font-size: 0.9rem;
    color: #667eea;
    font-weight: 600;
    margin-bottom: 1rem;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.question-text {
    font-size: 1.2rem;
    line-height: 1.7;
    margin-bottom: 2rem;
    color: #2d3748;
    font-weight: 400;
}

.options-container {
    margin-bottom: 2rem;
}

.option {
    background: #f7fafc;
    border: 2px solid #e2e8f0;
    border-radius: 12px;
    padding: 1rem 1.5rem;
    margin-bottom: 1rem;
    cursor: pointer;
    transition: all 0.3s ease;
    display: flex;
    align-items: flex-start;
}

.option:hover {
    border-color: #667eea;
    background: #edf2f7;
    transform: translateX(4px);
}

.option.selected {
    border-color: #667eea;
    background: #e6fffa;
}

.option.correct {
    border-color: #48bb78;
    background: #f0fff4;
}

.option.incorrect {
    border-color: #f56565;
    background: #fed7d7;
}

.option-letter {
    background: #667eea;
    color: white;
    width: 28px;
    height: 28px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 600;
    margin-right: 1rem;
    flex-shrink: 0;
    font-size: 0.9rem;
}

.option.correct .option-letter {
    background: #48bb78;
}

.option.incorrect .option-letter {
    background: #f56565;
}

.option-text {
    flex: 1;
    line-height: 1.5;
}

/* Feedback */
.feedback {
    background: #f7fafc;
    border-radius: 12px;
    padding: 1.5rem;
    margin-bottom: 2rem;
    border-left: 4px solid #667eea;
}

.feedback-content {
    display: flex;
    align-items: flex-start;
}

.feedback-icon {
    width: 24px;
    height: 24px;
    border-radius: 50%;
    margin-right: 1rem;
    flex-shrink: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: bold;
    color: white;
}

.feedback.correct {
    border-left-color: #48bb78;
    background: #f0fff4;
}

.feedback.correct .feedback-icon {
    background: #48bb78;
}

.feedback.incorrect {
    border-left-color: #f56565;
    background: #fed7d7;
}

.feedback.incorrect .feedback-icon {
    background: #f56565;
}

.feedback-text {
    flex: 1;
    line-height: 1.6;
}

/* Navigation */
.navigation {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 1rem;
}

/* Results Screen */
.results-content {
    text-align: center;
    max-width: 500px;
    margin: 0 auto;
    padding: 2rem 0;
}

.score-circle {
    width: 150px;
    height: 150px;
    border-radius: 50%;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    margin: 0 auto 2rem;
    color: white;
    box-shadow: 0 10px 30px rgba(102, 126, 234, 0.3);
}

.score-number {
    font-size: 2.5rem;
    font-weight: 700;
}

.score-label {
    font-size: 0.9rem;
    opacity: 0.9;
}

.performance-analysis h2 {
    margin-bottom: 1.5rem;
    color: #2d3748;
}

.stats {
    background: #f7fafc;
    border-radius: 12px;
    padding: 1.5rem;
    margin-bottom: 2rem;
}

.stat {
    display: flex;
    justify-content: space-between;
    margin-bottom: 0.8rem;
}

.stat:last-child {
    margin-bottom: 0;
}

.stat-label {
    color: #4a5568;
}

.stat-value {
    font-weight: 600;
    color: #2d3748;
}

.performance-message {
    font-size: 1.1rem;
    margin-bottom: 2rem;
    padding: 1rem;
    border-radius: 8px;
    font-weight: 500;
}

.performance-message.excellent {
    background: #f0fff4;
    color: #22543d;
    border: 1px solid #9ae6b4;
}

.performance-message.good {
    background: #fffaf0;
    color: #744210;
    border: 1px solid #fbd38d;
}

.performance-message.needs-improvement {
    background: #fed7d7;
    color: #742a2a;
    border: 1px solid #fc8181;
}

.action-buttons {
    display: flex;
    gap: 1rem;
    justify-content: center;
    flex-wrap: wrap;
}

/* Review Screen */
.review-content {
    max-width: 800px;
    margin: 0 auto;
}

.review-content h2 {
    text-align: center;
    margin-bottom: 2rem;
    color: #2d3748;
}

.review-list {
    margin-bottom: 2rem;
}

.review-item {
    background: #f7fafc;
    border-radius: 12px;
    padding: 1.5rem;
    margin-bottom: 1.5rem;
    border-left: 4px solid #e2e8f0;
}

.review-item.correct {
    border-left-color: #48bb78;
    background: #f0fff4;
}

.review-item.incorrect {
    border-left-color: #f56565;
    background: #fed7d7;
}

.review-question {
    font-weight: 600;
    margin-bottom: 1rem;
    color: #2d3748;
}

.review-answer {
    margin-bottom: 0.5rem;
}

.review-answer.user {
    color: #4a5568;
}

.review-answer.correct {
    color: #22543d;
    font-weight: 500;
}

/* Responsive Design */
@media (max-width: 768px) {
    .container {
        padding: 10px;
    }
    
    .title {
        font-size: 2rem;
    }
    
    .screen {
        padding: 1.5rem;
    }
    
    .question-text {
        font-size: 1.1rem;
    }
    
    .navigation {
        flex-direction: column;
        gap: 0.5rem;
    }
    
    .navigation .btn {
        width: 100%;
    }
    
    .action-buttons {
        flex-direction: column;
    }
    
    .action-buttons .btn {
        width: 100%;
    }
}

@media (max-width: 480px) {
    .option {
        padding: 0.8rem 1rem;
    }
    
    .option-letter {
        width: 24px;
        height: 24px;
        font-size: 0.8rem;
    }
    
    .score-circle {
        width: 120px;
        height: 120px;
    }
    
    .score-number {
        font-size: 2rem;
    }
}