a.back-to-top {
    display: none;
    width: 60px;
    height: 60px;
    text-indent: -9999px;
    position: fixed;
    z-index: 999;
    right: 20px;
    bottom: 20px;
    background: #27AE61 url("../images/up-arrow.png") no-repeat center 43%;
    -webkit-border-radius: 30px;
    -moz-border-radius: 30px;
    border-radius: 30px;
}