#back-to-top{display:none;position:fixed;bottom:20px;right:20px;z-index:99;font-size:18px;border:none;outline:none;background-color:rgba(0,0,0,.5);color:#fff;cursor:pointer;padding:15px;border-radius:4px}#back-to-top:hover{background-color:rgba(0,0,0,.8)}