body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
    background-color: #f4f4f9;
    color: #333;
}
header {
    background-color: #4CAF50;
    color: white;
    text-align: center;
    padding: 1em 0;
}
nav ul {
    list-style: none;
    padding: 0;
    text-align: center;
}
nav ul li {
    display: block; /* 使列表项垂直排列 */
    margin: 10px auto;
}
nav ul li a {
    text-decoration: none;
    font-size: 18px;
    padding: 10px 16px;
    border-radius: 5px;
    background-color: #4CAF50;
    color: white;
    display: block;
    width: 200px;
    text-align: center;
    margin: auto;
}
nav ul li a:hover {
    background-color: #45a049;
}
footer {
    text-align: center;
    margin-top: 20px;
    font-size: 0.8em;
}