.back-to-top {
    margin: 0 1rem 4rem 0;
    text-align: right;
    height: 1.5rem;
    opacity: 1;
}

.back-to-top-hidden {
    transition-property: margin,height,opacity;
    transition-duration: 500ms,500ms,200ms;
    transition-timing-function: ease-in;
    
    margin: 0;
    height: 0;
    opacity: 0;
    overflow: hidden;
}