User blog comment:Mouseinphilly/Trick....Treat...Halloween Backgrounds, Please!/@comment-961279-20140823055508

When designing the background, what seems to work best is to start with a picture that's about 1500x1100. For some reason, the wiki can contract and expand a large picture like this, but it has problems expanding pictures that are a lot smaller in width. The sidebars are 170 pixels wide, so anything in between them is what will show through the main page when the transparency is turned on. The middle of the background has to be left empty since that's the point where the wiki splits or contracts the image to fit the web browser you're using. And the largest monitor most people have has a vertical resolution of about 1080, but can be shorter, so anything at the bottom of the image needs to be minimal in case it isn't displayed by their web browser.