body {
    font-family: Arial, sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    background-color: #f0f0f0;
}

#countdown {
    font-size: 1em; /* 将字体大小设置为1em，可以根据需要进一步调整 */
    color: #333;
}