#backToTop {
    display: inline-block;
    position: fixed;
    bottom: 30px;
    right: 30px;
    transition: background-color .3s,
    opacity .5s, visibility .5s;
    visibility: hidden;
    z-index: 1000;
}
#backToTop::after {
    line-height: 50px;
}
#backToTop.show {
    opacity: 1;
    visibility: visible;
}