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

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

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 2rem;
}

.navbar {
    background: rgba(255,255,255,0.95);
    backdrop-filter: blur(10px);
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
    padding: 1rem 2rem;
    position: sticky;
    top: 0;
    z-index: 1000;
}

.nav-container {
    max-width: 1200px;
    margin: 0 auto;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.nav-brand {
    font-size: 1.5rem;
    font-weight: 700;
    color: #667eea;
    text-decoration: none;
}

.nav-links {
    display: flex;
    gap: 1.5rem;
    align-items: center;
}

.nav-links a {
    color: #666;
    text-decoration: none;
    padding: 0.5rem 1rem;
    border-radius: 8px;
    transition: all 0.3s;
}

.nav-links a:hover {
    background: #f0f0f0;
    color: #333;
}

.welcome-section {
    background: rgba(255,255,255,0.95);
    border-radius: 16px;
    padding: 2.5rem;
    margin-bottom: 2rem;
    text-align: center;
    box-shadow: 0 4px 20px rgba(0,0,0,0.1);
}

.welcome-section h1 {
    font-size: 2.5rem;
    background: linear-gradient(135deg, #667eea, #764ba2);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    margin-bottom: 0.5rem;
}

.welcome-section p {
    color: #666;
    font-size: 1.1rem;
    margin-bottom: 1rem;
}

.stats {
    background: #f8f9fa;
    padding: 0.75rem 1.5rem;
    border-radius: 8px;
    display: inline-block;
}

.lessons-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 1.5rem;
}

.lesson-card {
    background: rgba(255,255,255,0.95);
    border-radius: 16px;
    padding: 1.5rem;
    box-shadow: 0 4px 20px rgba(0,0,0,0.1);
    transition: transform 0.3s, box-shadow 0.3s;
    position: relative;
    overflow: hidden;
}

.lesson-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 8px 30px rgba(0,0,0,0.15);
}

.lesson-card.completed {
    border-left: 4px solid #28a745;
}

.lesson-badge {
    font-size: 0.75rem;
    font-weight: 600;
    color: #666;
    margin-bottom: 0.5rem;
}

.lesson-card h3 {
    font-size: 1.25rem;
    margin-bottom: 0.5rem;
    color: #333;
}

.lesson-level {
    color: #667eea;
    font-weight: 600;
    font-size: 0.9rem;
    margin-bottom: 1rem;
}

.lesson-preview {
    color: #666;
    font-size: 0.95rem;
    line-height: 1.5;
    margin-bottom: 1rem;
}

.lesson-actions {
    display: flex;
    gap: 0.5rem;
}

.btn-primary {
    background: linear-gradient(135deg, #667eea, #764ba2);
    color: white;
    padding: 0.5rem 1.5rem;
    border-radius: 8px;
    text-decoration: none;
    font-weight: 600;
    transition: transform 0.2s;
    display: inline-block;
    border: none;
    cursor: pointer;
    font-size: 1rem;
}

.btn-primary:hover {
    transform: scale(1.05);
}

.lesson-container {
    background: rgba(255,255,255,0.95);
    border-radius: 16px;
    padding: 2.5rem;
    box-shadow: 0 4px 20px rgba(0,0,0,0.1);
}

.lesson-header {
    margin-bottom: 2rem;
    border-bottom: 2px solid #f0f0f0;
    padding-bottom: 1rem;
}

.btn-back {
    display: inline-block;
    color: #667eea;
    text-decoration: none;
    margin-bottom: 1rem;
    font-weight: 500;
}

.btn-back:hover {
    text-decoration: underline;
}

.lesson-header h1 {
    font-size: 2rem;
    color: #333;
    margin-bottom: 0.5rem;
}

.completion-badge {
    background: #28a745;
    color: white;
    padding: 0.5rem 1rem;
    border-radius: 8px;
    display: inline-block;
    margin-top: 1rem;
}

.lesson-content {
    line-height: 1.8;
    font-size: 1.05rem;
    margin-bottom: 2rem;
}

.lesson-content h2 {
    color: #667eea;
    margin: 1.5rem 0 0.5rem 0;
}

.lesson-content h3 {
    color: #764ba2;
    margin: 1rem 0 0.5rem 0;
}

.lesson-content ul {
    margin: 0.5rem 0 1rem 1.5rem;
}

.lesson-content li {
    margin-bottom: 0.25rem;
}

.quiz-section {
    background: #f8f9fa;
    border-radius: 12px;
    padding: 2rem;
    margin-top: 2rem;
}

.quiz-section h2 {
    color: #333;
    margin-bottom: 1.5rem;
}

#question-container {
    background: white;
    border-radius: 12px;
    padding: 1.5rem;
    margin-bottom: 1rem;
}

#question-text {
    font-size: 1.2rem;
    font-weight: 600;
    margin-bottom: 1.5rem;
    color: #333;
}

#options-container {
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
}

.option-btn {
    background: white;
    border: 2px solid #e0e0e0;
    padding: 0.75rem 1.5rem;
    border-radius: 8px;
    cursor: pointer;
    font-size: 1rem;
    transition: all 0.3s;
    text-align: left;
}

.option-btn:hover:not(:disabled) {
    border-color: #667eea;
    background: #f0f4ff;
}

.option-btn.selected {
    border-color: #667eea;
    background: #e8edff;
}

.option-btn.correct {
    border-color: #28a745;
    background: #d4edda;
    color: #155724;
}

.option-btn.wrong {
    border-color: #dc3545;
    background: #f8d7da;
    color: #721c24;
}

.option-btn:disabled {
    cursor: not-allowed;
    opacity: 0.7;
}

#feedback-container {
    margin-top: 1.5rem;
    padding: 1rem;
    border-radius: 8px;
    display: none;
}

#feedback-container.show {
    display: block;
}

#feedback-container.correct {
    background: #d4edda;
    border: 1px solid #c3e6cb;
    color: #155724;
}

#feedback-container.wrong {
    background: #f8d7da;
    border: 1px solid #f5c6cb;
    color: #721c24;
}

#quiz-progress {
    text-align: center;
    color: #666;
    font-weight: 500;
}

@media (max-width: 768px) {
    .container {
        padding: 1rem;
    }
    
    .welcome-section h1 {
        font-size: 1.8rem;
    }
    
    .lessons-grid {
        grid-template-columns: 1fr;
    }
    
    .lesson-container {
        padding: 1.5rem;
    }
    
    .quiz-section {
        padding: 1rem;
    }
}