#backtotop {
    background: url(../images/backtotop.png) no-repeat center center;
    border: 0;
    bottom: 5rem;
    cursor: pointer;
    display: none;
    height: 70px;
    position: fixed;
    right: 20px;
    text-indent: -9999px;
    width: 70px;
    z-index: 300;
}

#backtotop:hover {
    opacity: 0.8;
}

#backtotop:focus {
    opacity: 0.6;
    outline: none;
}

@media (-webkit-min-device-pixel-ratio: 2),
(min-resolution: 192dpi) {
    #backtotop {
        background: url(../images/backtotop2x.png) no-repeat center center;
        background-size: 70px 70px;
    }
}