Insufficient documentation 
An explanation for this variable is missing. The reference to "See MediaWiki:Common.css" is not helping. Is "MediaWiki:Common.css" equal or different to the "site's stylesheets"? --G.Hagedorn 13:04, 12 March 2009 (UTC)
I'll +1 that. Please document further. Also, MediaWiki:Common.css was moved to MediaWiki:Gadget-site.css without leaving a redirect. Does that affect the functionality of this variable? - Frenz242 (talk) 05:26, 9 April 2013 (UTC)
I agree, this documentation is severely Lacking
I'm having trouble with common.css. Was hoping this variable might do something. Seems there is no way to tell what the hell it is for.
- This variable tells MW whether to use MediaWiki:Common.css at all. Set it to false if you are only getting your styles from somewhere else (e.g. main.css, or any other css source called from your skin). rotsee 22:40, 18 June 2011 (UTC)