body {
    font-family: Arial, sans-serif;
    background-image: url('https://www.ngoisaoso.vn/uploads/news/2015/03/19/Best-Website-Background-Images14.jpg'); 
    background-size: cover; 
    background-position: center; 
    background-attachment: fixed; 
    color: #333;
    padding: 0;
    margin: 0;

    
    font-family: Arial, sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background-color: #e0f7fa;
}
.navbar {
    background-color: #5d9aeef6;
    padding: 10px;
    display: flex;
    position: fixed;
    top: 0;
    z-index: 1000;
}
.navbar a {
    color: white;
    padding: 14px 20px;
    text-decoration: none;
    font-size: 18px;
    margin: 0 15px;
}

.navbar a:hover {
    background-color: #383939;
    border-radius: 4px;
}
.container {
    max-width: 1200px;
    margin: 80px auto 0 auto;
    text-align: center;
}
h1 {
    font-size: 2.5rem;
    margin-bottom: 20px;
}
.grid {
    display: grid;
    grid-template-columns: repeat(3,1fr);
    gap: 20px;
    margin-top: 30px;
    justify-items: center;
}
.card {
    background-image: url(https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcTf-wQqg6ZJKV6RJV514bbntXgdNKRbNSjRuSjmRhKBs3TvuMmb8ToyhpoK3ANDklO8yuM&usqp=CAU);
    background-size: cover;
    background-position: center; 
    background-color: white;
    border: 1px solid #ddd;
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
    text-align: center;
    width: 100%;
    flex-direction: column;
    max-width: 250px;
    justify-content: space-between;
    height: 200px;
    display: flex ;
}
.card img {
    width: 30px; 
    height: auto; 
    margin-bottom: 10px;
    display: block;
    margin-left: auto;
    margin-right: auto;
}
.card button {
    padding: 10px 20px;
    background-color: #007bff;
    color: white;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    font-size: 1rem;
    width: 100%;
    margin-top: auto;

}
.card 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%;
    }
}