/* formatting this so you can just copy paste without having to sort through to delete me yapping ^_ anyways!! */

#page { background: url(LinkToImageHere.png)!important; } /* the div used for your bg doesn't have a class from what I could find, so you have to use the id (page) and the id selector for this. also do not remove the !important thing!! in the default css the background already has a set style, so you need to override it and using this method is the best way I know how. You may also be able to just put url(link) in the box in settings without actually messing with the css, but I haven't tested images with variables (which is what the default css for this uses) so I went with re-writing the css entirely via !important */

url()