#back-top {
    margin:0;
    padding:0;
        position: fixed;
        bottom: 100px;
        margin-left: 0px;
        clear: both;
    display:block;
 
}
#back-top a {
    padding: 0;
    margin: 0;
    height: 40px;
    width: 40px;
    display: block;
}
/* arrow icon (span tag) */
#back-top span {
    float:right;
        width: 40px;
        height: 40px;
        display: block;
        margin-bottom: 7px;
        background: url(/images/button.png) no-repeat center center;
        /* rounded corners */

}
#back-top a:hover span {
    background: url(/images/buttonh.png) no-repeat center center;
}