#btn-return-top {
    font-size: 24px;
    line-height: 24px;
    color: #FFF;
    right: -60px;
    bottom: 50px;
    opacity: 0;
    -webkit-border-radius: 3px;
    -moz-border-radius: 3px;
    border-radius: 3px;
    background-color: #ccc;
    background-color: rgba(0, 0, 0, 0.2);
    padding: 10px 9px 15px 9px;
    position: fixed;
    z-index: 100;
    transition: all 0.2s ease-in-out;
    -webkit-transition: all 0.2s ease-in-out;
    -moz-transition: all 0.2s ease-in-out;
    -ms-transition: all 0.2s ease-in-out;
    -o-transition: all 0.2s ease-in-out;
}

#btn-return-top:hover {
    background-color: rgba(0, 0, 0, 0.4);
}