* {
    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;
    line-height: 1.6;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 20px;
}

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

header h1 {
    font-size: 3rem;
    font-weight: 700;
    margin-bottom: 10px;
    text-shadow: 2px 2px 4px rgba(0,0,0,0.3);
}

.subtitle {
    font-size: 1.2rem;
    opacity: 0.9;
    font-weight: 300;
}

/* Navigation */
.navigation {
    display: flex;
    justify-content: center;
    gap: 10px;
    margin-bottom: 30px;
    flex-wrap: wrap;
}

.nav-btn {
    background: rgba(255, 255, 255, 0.2);
    border: 2px solid rgba(255, 255, 255, 0.3);
    color: white;
    padding: 12px 24px;
    border-radius: 25px;
    cursor: pointer;
    font-size: 1rem;
    font-weight: 500;
    transition: all 0.3s ease;
    backdrop-filter: blur(10px);
}

.nav-btn:hover {
    background: rgba(255, 255, 255, 0.3);
    transform: translateY(-2px);
}

.nav-btn.active {
    background: white;
    color: #667eea;
    box-shadow: 0 4px 15px rgba(0,0,0,0.2);
}

/* Content Sections */
.content-section {
    display: none;
    background: white;
    border-radius: 20px;
    padding: 40px;
    box-shadow: 0 10px 30px rgba(0,0,0,0.1);
    animation: fadeIn 0.5s ease;
}

.content-section.active {
    display: block;
}

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

.content-section h2 {
    color: #667eea;
    font-size: 2.5rem;
    margin-bottom: 30px;
    text-align: center;
    font-weight: 600;
}

/* Theory Section */
.theory-card {
    background: linear-gradient(135deg, #f093fb 0%, #f5576c 100%);
    color: white;
    padding: 30px;
    border-radius: 15px;
    margin-bottom: 30px;
    box-shadow: 0 5px 15px rgba(0,0,0,0.1);
}

.theory-card h3 {
    font-size: 1.5rem;
    margin-bottom: 15px;
    font-weight: 600;
}

.formula {
    background: rgba(255, 255, 255, 0.2);
    padding: 15px;
    border-radius: 10px;
    text-align: center;
    font-size: 1.5rem;
    font-weight: 600;
    margin-top: 15px;
    backdrop-filter: blur(10px);
}

.theory-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 20px;
    margin-bottom: 30px;
}

.theory-item {
    background: #f8f9fa;
    padding: 25px;
    border-radius: 15px;
    border-left: 5px solid #667eea;
    transition: transform 0.3s ease;
}

.theory-item:hover {
    transform: translateY(-5px);
    box-shadow: 0 5px 15px rgba(0,0,0,0.1);
}

.theory-item h4 {
    color: #667eea;
    font-size: 1.3rem;
    margin-bottom: 15px;
    font-weight: 600;
}

.theory-item ul {
    list-style: none;
    padding-left: 0;
}

.theory-item li {
    background: white;
    margin: 8px 0;
    padding: 10px 15px;
    border-radius: 8px;
    font-weight: 500;
    box-shadow: 0 2px 5px rgba(0,0,0,0.05);
}

.theory-card.highlight {
    background: linear-gradient(135deg, #4facfe 0%, #00f2fe 100%);
}

/* Practice Section */
.practice-container {
    max-width: 800px;
    margin: 0 auto;
}

.exercise-card {
    background: #f8f9fa;
    padding: 30px;
    border-radius: 15px;
    margin-bottom: 30px;
    border: 2px solid #e9ecef;
}

.exercise-card h3 {
    color: #667eea;
    font-size: 1.5rem;
    margin-bottom: 20px;
    font-weight: 600;
}

.exercise-grid {
    display: grid;
    gap: 20px;
}

.exercise-item {
    display: flex;
    align-items: center;
    gap: 15px;
    background: white;
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.05);
}

.problem {
    font-size: 1.2rem;
    font-weight: 600;
    color: #333;
    min-width: 80px;
}

.answer-input {
    width: 80px;
    padding: 10px;
    border: 2px solid #ddd;
    border-radius: 8px;
    font-size: 1rem;
    text-align: center;
    transition: border-color 0.3s ease;
}

.answer-input:focus {
    outline: none;
    border-color: #667eea;
}

.check-btn {
    background: #667eea;
    color: white;
    border: none;
    padding: 10px 20px;
    border-radius: 8px;
    cursor: pointer;
    font-weight: 500;
    transition: background 0.3s ease;
}

.check-btn:hover {
    background: #5a6fd8;
}

.result {
    font-weight: 600;
    min-width: 60px;
}

.result.correct {
    color: #28a745;
}

.result.incorrect {
    color: #dc3545;
}

/* True/False Section */
.true-false-grid {
    display: grid;
    gap: 20px;
}

.tf-item {
    display: flex;
    align-items: center;
    gap: 15px;
    background: white;
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.05);
}

.statement {
    font-size: 1.1rem;
    font-weight: 500;
    flex: 1;
}

.tf-buttons {
    display: flex;
    gap: 10px;
}

.tf-btn {
    padding: 8px 16px;
    border: 2px solid #ddd;
    background: white;
    border-radius: 6px;
    cursor: pointer;
    font-weight: 500;
    transition: all 0.3s ease;
}

.tf-btn:hover {
    border-color: #667eea;
    background: #f8f9ff;
}

.tf-btn.correct {
    background: #28a745;
    color: white;
    border-color: #28a745;
}

.tf-btn.incorrect {
    background: #dc3545;
    color: white;
    border-color: #dc3545;
}

.tf-result {
    font-weight: 600;
    min-width: 60px;
}

.reset-btn {
    background: #6c757d;
    color: white;
    border: none;
    padding: 15px 30px;
    border-radius: 10px;
    cursor: pointer;
    font-size: 1rem;
    font-weight: 500;
    transition: background 0.3s ease;
    display: block;
    margin: 0 auto;
}

.reset-btn:hover {
    background: #5a6268;
}

/* Quiz Section */
.quiz-container {
    max-width: 800px;
    margin: 0 auto;
}

.quiz-info {
    text-align: center;
    margin-bottom: 30px;
    background: #f8f9fa;
    padding: 20px;
    border-radius: 15px;
}

.progress-bar {
    width: 100%;
    height: 10px;
    background: #e9ecef;
    border-radius: 5px;
    margin: 15px 0;
    overflow: hidden;
}

.progress-fill {
    height: 100%;
    background: linear-gradient(90deg, #667eea, #764ba2);
    width: 0%;
    transition: width 0.3s ease;
}

.progress-text {
    font-weight: 600;
    color: #667eea;
}

.question {
    background: white;
    padding: 30px;
    border-radius: 15px;
    margin-bottom: 20px;
    box-shadow: 0 5px 15px rgba(0,0,0,0.1);
    border: 2px solid transparent;
    transition: all 0.3s ease;
}

.question:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 25px rgba(0,0,0,0.15);
}

.question h3 {
    color: #667eea;
    margin-bottom: 15px;
    font-size: 1.3rem;
}

.question p {
    font-size: 1.1rem;
    margin-bottom: 20px;
    font-weight: 500;
}

.options {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: 10px;
}

.option {
    padding: 15px 20px;
    border: 2px solid #ddd;
    background: white;
    border-radius: 10px;
    cursor: pointer;
    font-size: 1rem;
    font-weight: 500;
    transition: all 0.3s ease;
}

.option:hover {
    border-color: #667eea;
    background: #f8f9ff;
}

.option.correct {
    background: #28a745;
    color: white;
    border-color: #28a745;
}

.option.incorrect {
    background: #dc3545;
    color: white;
    border-color: #dc3545;
}

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

/* Quiz Results */
.quiz-results {
    text-align: center;
    background: white;
    padding: 40px;
    border-radius: 15px;
    box-shadow: 0 5px 15px rgba(0,0,0,0.1);
}

.score-display {
    font-size: 2rem;
    margin: 20px 0;
}

.score-value {
    font-weight: 700;
    color: #667eea;
}

.score-message {
    font-size: 1.2rem;
    margin: 20px 0;
    padding: 15px;
    border-radius: 10px;
    font-weight: 500;
}

.score-message.excellent {
    background: #d4edda;
    color: #155724;
    border: 1px solid #c3e6cb;
}

.score-message.good {
    background: #d1ecf1;
    color: #0c5460;
    border: 1px solid #bee5eb;
}

.score-message.needs-improvement {
    background: #f8d7da;
    color: #721c24;
    border: 1px solid #f5c6cb;
}

.retake-btn {
    background: #667eea;
    color: white;
    border: none;
    padding: 15px 30px;
    border-radius: 10px;
    cursor: pointer;
    font-size: 1rem;
    font-weight: 500;
    transition: background 0.3s ease;
}

.retake-btn:hover {
    background: #5a6fd8;
}

/* Responsive Design */
@media (max-width: 768px) {
    .container {
        padding: 10px;
    }
    
    header h1 {
        font-size: 2rem;
    }
    
    .content-section {
        padding: 20px;
    }
    
    .theory-grid {
        grid-template-columns: 1fr;
    }
    
    .exercise-item {
        flex-direction: column;
        text-align: center;
        gap: 10px;
    }
    
    .tf-item {
        flex-direction: column;
        text-align: center;
        gap: 10px;
    }
    
    .options {
        grid-template-columns: 1fr;
    }
    
    .navigation {
        flex-direction: column;
        align-items: center;
    }
    
    .nav-btn {
        width: 100%;
        max-width: 300px;
    }
}