body {
    font-family: Arial, sans-serif;
    margin: 0;
    background: #f4f6f9;
}

header {
    background: #1e3a8a;
    color: white;
    text-align: center;
    padding: 30px;
}

.lesson-list {
    max-width: 900px;
    margin: 40px auto;
    padding: 20px;
}

.lesson-card {
    display: block;
    background: white;
    padding: 25px;
    margin-bottom: 20px;
    border-radius: 8px;
    text-decoration: none;
    color: black;
    box-shadow: 0 5px 15px rgba(0,0,0,0.1);
}

.lesson-card:hover {
    background: #e0e7ff;
}

.content {
    max-width: 900px;
    margin: 30px auto;
    background: white;
    padding: 30px;
    border-radius: 8px;
}

audio {
    width: 100%;
    margin-top: 10px;
}

.btn {
    display: inline-block;
    margin-top: 15px;
    padding: 10px 15px;
    background: #2563eb;
    color: white;
    text-decoration: none;
    border-radius: 6px;
}

.btn:hover {
    background: #1d4ed8;
}

.navigation {
    margin-top: 30px;
}

.top-btn {
    position: fixed;
    bottom: 20px;
    right: 20px;
    padding: 10px 15px;
    background: #2563eb;
    color: white;
    border: none;
    border-radius: 50px;
    cursor: pointer;
}

footer {
    text-align: center;
    padding: 20px;
    background: #1e3a8a;
    color: white;
    margin-top: 40px;
}