Board Thread:Support Requests - Designing Your Wiki/@comment-33220655-20180503040552

So i'm trying to change the backround for a wikia, but when uploading the image it says "incorrect file size", now I get that the image must be less than 300 kilobytes, so how do wiki's such as this one (http://danganronpa.wikia.com/wiki/Danganronpa_Wiki) have such beautiful backgrounds, are those 300 kb's too? If so, how do you get an image to that size? 