stadtreporter Hi. It worked, but You haven't activated CSS Override in template's settings.
I've also changed the code a little adding extra selector to be sure all browsers will accept it.
.gkHighlighterItem[style="display:block;opacity:1;top:0px;"],
.gkHighlighterItem[style="display: block; opacity: 1; top: 0px;"] {
z-index: 10;
}