#back-top {position: fixed;bottom: 30px;z-index:9999;left:50%;margin-left:600px;}
#back-top a:hover {color:#79ec3e;}
#back-top span {width:35px;height:20px;display: block;margin-bottom: 7px;background:url(up-arrow.png) no-repeat left 0px;}
#back-top a:hover span { background-position:left -34px;}