Reply To: Slider on the catalog page (general shop page)

Try to add the following code snippet to the Custom CSS area in Theme Settings to change categories background

.cat-design-default .category-title {
	color: white!important;
	background: #0054ac;
	padding: 8px 25px;
}

So what do you want to do with the categories menu? Show it on the shop page only? In this case, it will overlap the sidebar.