#nav-top {
    position: fixed; right: var(--gap-y); bottom: var(--gap-y);
    padding: 0 0.1em;
    border-radius: 50%;
    background-color: var(--color-1); color: var(--color-on-1);
    opacity: 80%;
    transition: opacity 1s ease-out;
    font-size: 3rem;
}
#nav-top.hidden { opacity: 0%; }