body{
     background-image:url(https://images.cnblogs.com/cnblogs_com/blogs/776052/galleries/2245094/o_221118044602_v2-98bf3e2af93f1937fb59361f87394f16_r.jpg);
     background-attachment:fixed; //设置背景图像是否固定或者随着页面的其余部分滚动
}
#home{
    opacity:0.5; //背景透明度设置，值越低越透明 0~1
}
//返回顶部按钮
#back-to-top {
    background-color: #8bcc99;
    bottom: 10px;
    box-shadow: 0 0 6px #72a072;
    padding: 5px 10px;
    position: fixed;
    right: 50px;
    border-radius: 8px;
    opacity: 0.7;
    cursor: pointer;
}