.galleria-lightbox-nextholder {
    /* Originally .galleria-lightbox-nextholder has the same z-index as .galleria-lightbox-close (99999), resulting in
    the effect, that sometimes the next image will be shown in the lightbox instead of closing it.
    We hav to use !important, as these style are defined inline in the page. */
    z-index: 99998 !important;
}