Needing to edit location and style of gallery arrows

The Arrows that are pre-programmed are causing viability issues with images in my gallery. (as pictured on left.) need to move those arrows and tweak them so the visibility is more clear and consistent. (adding shadow etc… like as pictured on the right of this image.) I remember I used to be able to futz with it… including bumping the arrow size up to take over that entire half of the gallery page and turning up the opacity to basically have my image arrows function correctly like as if they were the actual buttons. … but now I cannot seem to locate such tools or even elements in a layer to fidget with them… please halp!