#back-to-top{position:fixed;bottom:40px;right:40px;z-index:9999;width:32px;height:32px;text-align:center;line-height:30px;background:#000;color:#fff;cursor:pointer;border:0;border-radius:2px;text-decoration:none;transition:opacity .2s ease-out;opacity:0}#back-to-top:hover{background:#555;color:#fff}#back-to-top.show{opacity:1}