#back-top {
        border: 1px solid rgb(192,192,192);
        position: fixed;
        bottom: 30px;
        z-index: 10000000000;
        margin-left: -150px;
        }

#back-top a {
        width: 108px;
        display: block;
        text-align: center;
        font: 11px/100% Arial, Helvetica, sans-serif;
        text-transform: uppercase;
        text-decoration: none;
        color: #bbb;

        /* transition */
        -webkit-transition: 1s;
        -moz-transition: 1s;
        transition: 1s;
        }

#back-top a:hover {
        color: #000;
        }
        
/* arrow icon (span tag) */
#back-top span {
        width: 108px;
        height: 108px;
        display: block;
        margin-bottom: 7px;
        background: #ddd url(/img/up-arrow.png) no-repeat center center;
        /* rounded corners */
        -webkit-border-radius: 15px;
        -moz-border-radius: 15px;
        border-radius: 15px;
        /* transition */
        -webkit-transition: 1s;
        -moz-transition: 1s;
        transition: 1s;
        }
        
#back-top a:hover span {
        background-color: #777;
        }