.go-top {
    position: fixed;
    right: 5px;
    bottom: 150px;
    width: 51px;
    z-index: 999;
    height: 51px;
    display: none;
}

#go-top a {
    background: url(gotop.png) no-repeat 0 0;
    width: 51px;
    height: 51px;
    overflow: hidden;
    text-indent: -2000em;
    display: block;
}

    #go-top a:hover {
        background-position: 0 -51px;
    }