.back-to-top {
    position: fixed;
    right: 60px;
    bottom: 60px;
    width: 60px;
    height: 60px;
    border-radius:  50%;
    background-image: url('../gfx/arrow_up.png');
    background-size: cover;
    background-position: center;
    z-index: 999999;
}