python-gallery/gallery/user/themes/default/buttons/up.scss

#topButton {
    margin: 0;
    padding: 0.25rem;

    width: 3rem;
    height: 3rem;

    position: fixed;
    bottom: 0.75rem;
    right: -3rem;

    display: flex; // hidden
    justify-content: center;
    align-items: center;

    border-radius: 50%;
    background-color: $black300;
    opacity: 0; // hidden

    z-index: 2;

    cursor: pointer;

    transition: all 0.2s cubic-bezier(.86, 0, .07, 1);

    &:hover {
        background-color: $black200;
        color: $green;
    }
}