User blog comment:DaNASCAT/Technical Update: December 11, 2012/@comment-3441771-20121212034223/@comment-188432-20121212180348

Also, I'm not entirely sure that the loss of the transparency slider can be fully compensated for. Again, maybe it's my eyes playing tricks on me, but it seems to me that when I've deployed my own transparency through Wikia.css, and then I use the transparency slider, I get a multiplicative transparency that doesn't occur when I remark out the transparency in my Wikia.css and just go with the Theme Designer alone.

How you would achieve this double transparency, using only the tools that are freely editable by admin, I dunno.