Background image not displaying

I can’t get a custom background to display. I’ve tried uploading a few different files, changing the way in which it repeats, where it’s centered, etc., and nothing. It defaults to white, and since I removed the original one that came with Themolio, it also won’t let me change the background color.

Is there a way to override this problem in the code? If so, could someone point me to what I’d need to change?