One interesting thing is that themes default to the "main" theme.
If an image reference in the application does not exist in a theme, the image is served from the default theme.
This is to make it easier to make themes. One can start with a fairly "thin" theme and enhance it over time by adding new images and improvements.
= Making Theme Without CSS coding =
<nowiki>Userstyles.org</nowiki> is the home of a the Stylish Firefox extension. It is similar to greasemonkey in that it can change the look of a page on the fly. Although the advantage for theme coders is that it just modifies CSS so you can write your theme in the browser instead of writing it in a text editor and saving it then refreshing the page. Making theme development UBER fast.