My css editing wont work and Home Page Banner Spacing

On my site, aquaticjewels.net, I am trying to move two images over in the banners section to close up that white awkward space between the large banner “Aquarium Supplies” and the two smaller banners directly to the right of it. I tried editing the appearance, but when I click update nothing changes! I even started taking out pieces of the code just to see if I was inept, but nothing changed when I pressed update. I used an inspector element on my browser to see if I could home in on the code for that place, but it doesn’t even show the same code in the editor(difference betwixt html and css I assume). What do I need to do?