Issue with Upfront slider background and custom CSS

There's this code added to Region CSS (see region with three boxes, with people photos in the center of the page):

.upfront-region-center {
background: white;
border: 1px solid rgb(0, 179, 246, .3);
border-radius: 8px;
margin-top: 10px;
margin-bottom: 10px;

If there's a slider background added to the region, it "overrides" it and custom code effect "fades in" into background. Strangely, this only happens for logged in visitors.