:root {
    --primary: #2c3e50;
    --secondary: #3498db;
    --light: #ecf0f1;
    --dark: #2c3e50;
    --success: #2ecc71;
    --warning: #f39c12;
    --danger: #e74c3c;
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    line-height: 1.6;
    color: var(--dark);
    max-width: 1200px;
    margin: 0 auto;
    padding: 20px;
}

header {
    background-color: var(--primary);
    color: white;
    padding: 2rem;
    border-radius: 8px;
    margin-bottom: 2rem;
}

.main-nav {
    display: flex;
    gap: 1rem;
    margin-top: 1rem;
}

.main-nav a {
    color: white;
    text-decoration: none;
    padding: 0.5rem 1rem;
    border-radius: 4px;
    transition: background-color 0.3s;
}

.main-nav a:hover {
    background-color: var(--secondary);
}

.chapter-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 1.5rem;
    margin: 2rem 0;
}

.chapter-card {
    background-color: white;
    border: 1px solid #ddd;
    border-radius: 8px;
    padding: 1.5rem;
    transition: transform 0.3s, box-shadow 0.3s;
    text-decoration: none;
    color: inherit;
}

.chapter-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 10px 20px rgba(0,0,0,0.1);
}

pre {
    background-color: #f8f9fa;
    padding: 1rem;
    border-radius: 6px;
    overflow-x: auto;
    border-left: 4px solid var(--secondary);
}

code {
    font-family: 'Courier New', Courier, monospace;
    color: var(--danger);
}

.exercise {
    background-color: #e8f4fc;
    padding: 1.5rem;
    border-radius: 8px;
    margin: 2rem 0;
    border-left: 4px solid var(--secondary);
}

.exercise h3 {
    margin-top: 0;
    color: var(--primary);
}

footer {
    text-align: center;
    margin-top: 3rem;
    padding: 1rem;
    border-top: 1px solid #ddd;
}

/* Responsive Design */
@media (max-width: 768px) {
    .chapter-grid {
        grid-template-columns: 1fr;
    }
}