.back-top{position:fixed;right:10px;bottom:130px;z-index:5;background-color:#fff;border-radius:50%;box-shadow:0 0 10px 0 hsla(0,0%,72.9%,.33);width:50px;height:50px;text-align:center;line-height:45px;font-size:30px;cursor:pointer;color:#ccc}