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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background-color: #F9F9F9;
    color: #333;
    line-height: 1.6;
    padding: 20px;
}

header {
    text-align: center;
    margin-bottom: 40px;
    padding: 20px;
}

header h1 {
    color: #4A90E2;
    font-size: 2.5rem;
}

.back-btn {
    display: inline-block;
    padding: 10px 20px;
    background: #4A90E2;
    color: white;
    text-decoration: none;
    border-radius: 5px;
    margin-bottom: 20px;
    font-weight: bold;
}

.class-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 20px;
    max-width: 1000px;
    margin: 0 auto;
}

.class-btn {
    display: block;
    padding: 30px 20px;
    background: #50C878;
    color: white;
    text-align: center;
    text-decoration: none;
    font-size: 1.5rem;
    font-weight: bold;
    border-radius: 15px;
    transition: all 0.3s ease;
    box-shadow: 0 4px 8px rgba(0,0,0,0.1);
}

.class-btn:hover {
    background: #3CB371;
    transform: scale(1.05);
    box-shadow: 0 6px 12px rgba(0,0,0,0.15);
}

.lesson-card {
    background: white;
    padding: 25px;
    margin-bottom: 30px;
    border-radius: 10px;
    box-shadow: 0 4px 10px rgba(0,0,0,0.05);
    transition: transform 0.3s ease;
}

.lesson-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 6px 15px rgba(0,0,0,0.1);
}

.lesson-card h3 {
    color: #4A90E2;
    margin-bottom: 15px;
}

.resources ul {
    list-style: none;
}

.resources li {
    margin: 10px 0;
}

.resources a {
    color: #4A90E2;
    text-decoration: none;
    font-weight: 500;
    display: inline-block;
}

.resources a:hover {
    text-decoration: underline;
}

footer {
    text-align: center;
    margin-top: 50px;
    padding: 20px;
    color: #777;
    font-size: 0.9rem;
}