body {
    font-family: Arial, sans-serif;
    background-image: url(https://noithatbinhminh.com.vn/wp-content/uploads/2022/12/background-den-08.jpg);
    background-size: cover;
    background-repeat: no-repeat ;
    background-position: center;
    background-attachment: fixed;
    margin: 0;
    padding: 0;
}

.navbar {
    background-color: #161616;
    padding: 10px;
    text-align: center;
}
.navbar a {
    color: white;
    padding: 14px 20px;
    text-decoration: none;
    font-size: 18px;
    margin: 0 10px;
}

.navbar a:hover {
    background-color: #383939;
    border-radius: 4px;
}

.container {
    width: 80%;
    margin: 0 auto;
    text-align: center;
}

h1 {
    margin-top: 20px;
    font-size: 2.5em;
    color: #e8e8e8;
}

.materials-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 20px;
    margin-top: 30px;
}

.material-card {
    background-color: rgba(244, 239, 239, 0.764);
    background-image: url(https://haycafe.vn/wp-content/uploads/2022/05/Background-xam-den.jpg);
    background-size: cover;
    background-repeat: no-repeat ;
    background-position: center;
    background-attachment: fixed;
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0 4px 8px rgba(0,0,0,0.1);
    transition: transform 0.2s ease;    
}

.material-card:hover {
    transform: translateY(-10px);
}

.icon {
    font-size: 40px;
    color: #083d76;
}

h3 {
    margin: 15px 0;
}

button {
    padding: 10px 20px;
    border: none;
    background-color: #000000;
    color: white;
    border-radius: 5px;
    cursor: pointer;
    transition: background-color 0.2s ease;
}

button:hover {
    background-color: #0056b3;
}
/*giao diện phần lesson
/* Mục con cho phần nội dung bài học */
.lesson-container {
    display: flex;
    margin: 20px;
    padding: 20px;
    background-color: #fff;
    border-radius: 10px;
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
}

/* Sidebar chứa danh sách bài học */
.sidebar {
    width: 25%;
    padding: 20px;
    background-color: #f9f9f9;
    border-right: 1px solid #ddd;
    border-radius: 10px 0 0 10px;
}

.sidebar ul {
    list-style-type: none;
    padding: 0;
}

.sidebar ul li {
    margin: 15px 0;
}

.sidebar ul li a {
    text-decoration: none;
    font-size: 18px;
    color: #007BFF;
    padding: 10px 15px;
    display: block;
    border-radius: 5px;
    transition: background-color 0.3s ease;
}

.sidebar ul li a:hover {
    background-color: #f0f0f0;
}

/* Phần nội dung chính của bài học */
.lesson-content {
    width: 75%;
    padding: 20px;
    background-color: #fff;
    border-radius: 0 10px 10px 0;
}

.lesson-content h2 {
    font-size: 28px;
    margin-bottom: 20px;
    color: #007BFF;
}

.lesson-content p {
    font-size: 16px;
    color: #555;
    line-height: 1.6;
}

.lesson-content ul {
    padding-left: 20px;
    margin: 20px 0;
}

.lesson-content ul li {
    font-size: 16px;
    margin-bottom: 10px;
}

/* Style cho các nút trong mục con */
.lesson-content button {
    padding: 10px 20px;
    font-size: 16px;
    border: none;
    background-color: #007bff;
    color: white;
    cursor: pointer;
    border-radius: 5px;
    transition: background-color 0.3s ease;
}

.lesson-content button:hover {
    background-color: #0056b3;
}

/* Nút 'Back to list' */
.back-to-list {
    display: inline-block;
    margin-top: 20px;
    padding: 10px 20px;
    background-color: #007BFF;
    color: white;
    border-radius: 5px;
    text-decoration: none;
    transition: background-color 0.2s ease;
}

.back-to-list:hover {
    background-color: #0056b3;
}

/* Responsive cho mục con */
@media (max-width: 768px) {
    .lesson-container {
        flex-direction: column;
    }

    .sidebar {
        width: 100%;
        border-right: none;
        border-bottom: 1px solid #ddd;
    }

    .lesson-content {
        width: 100%;
    }
}