div#goto-top {
    width: 2.5em;
    height: 2.5em;
    bottom: 10px;
    right: 10px;
    display: table;
    text-align: center;
    z-index: 9999999999;
    opacity: 0;
    transition: .6s;
    background-color: #33383c;
    color: #fff;
}

    div#goto-top.active {
        opacity: 1;
    }

    div#goto-top i.fa {
        display: table-cell;
        text-align: center;
    }