.back-to-top {
    display: none; /* 初始隐藏 */
    position: fixed;
    bottom: 20px;
    right: 20px;
    z-index: 100;
    background-color: #D8232A;
    color: white;
    border: none;
    border-radius: 5px;
    padding: 10px;
    cursor: pointer;
    font-size: 16px;
    width: 40px;
    height: 40px;
}

.back-to-top:hover {
    background-color: #e4171e;
}