Board Thread:Support Requests - Designing Your Wikia/@comment-10558422-20150703180341/@comment-5558012-20150703182128

Evacino wrote: So from what I am reading, some sources are saying using the Theme Designer splits the image in half and fills the center with a color and others say that it is necessary to use the CSS for a full background image. The image will be split for larger screen sizes if the image isn't over 2000px wide and the "no split" option isn't enabled (a great way to see the spilt is to make the middle color something bright and zoom out after you save it). Using CSS isn't recommended (or required in any fashion), but doing so bypasses the Themedesigner (likely used for wikis that have busy images and transparent content backgrounds; they can increase loading time and break with code updates).

The file size depends on the image. If it's a busy image and you have no transparency for the wiki, a great way to reduce the size is to cut out the middle of the image. Png files under 300kb are possible. Staff generally recommend you start with a 2000x900px canvas (if you are creating your background and not using a screen shot as you are more likely to make the file size limitation).