body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
    background-color: white;
}

header {
    background-color:#333;
    color: #fff;
    padding: 25px 0;
    text-align: center;
}
/* <导航栏> */
nav ul {
    list-style: none;
    padding: 0;
    margin: 0;
    display: flex;
    justify-content: center;
    background-color:#444;
    display: flex;
    justify-content: space-around;
    margin-top: -3px;
}

nav ul li {
    margin: 0 20px;
}

nav ul li a {
    color: #fff;
    text-decoration: none;
    font-weight: bold;
    font-size: 22px;
}

main {
    padding: 8px;
}

article {
    background-color: #fff;
    padding: 15px;
    margin-bottom: 20px;
    border-radius: 5px;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
}

footer {
    width: 100%;
    height: 10%;
    line-height: 40px;
    background-color: #333;
    color: #fff;
    text-align: center;
    font-size: 18px;
}