#back-to-top {
    bottom: 0;
    color: white;
    padding: 1px 1px;
    position: fixed;
    right: 50px;
    cursor: pointer;
}
body {
background:url(https://images.cnblogs.com/cnblogs_com/HuuuWnnn/1821261/o_220928095254_3056f8099da1dcf6232701b62b08e75d.jpeg
) fixed;
}