Well this was a nice, simple feature that had a hard-to-make implementation. Basically, the Wiki Style Manager shows the wiki headinclude and footer templates.
It also controls the Wiki CSS, which is divided into a number of templates, to make it easier to find the CSS selectors you're looking for. The fact that the CSS uses templates means that your changes will not be overwritten on upgrades and you can have different CSS for each of your forum's styles. In addition - and this was the crazy part to write, if your forum stores its CSS as files, the Wiki's CSS will also be saved to style-specific files in the vbulletin_css directory.
Getting the file to rewrite every time a wiki CSS template was possibly changed was the hard part. After considering all of vBulletin's methods, we also added support for the Advanced Product Management and Template Modification System mods.