Carsten of Langå, Denmark (BoardMod's Mod Author of the Year 2003, designer of YaBB's template editor and the new Y2.2 theme), has released a new mod called... the Tabbed Menu In CSS WYSIWYG Editor.  Here is Carsten's post:

There have been some comfusion over at yabbforum.com about the transparent menu tabs and title bars on board index. To try and make it easier to edit css i've packed up a fix to make those elements available in the css wysiwyg editor.
 
In the zip package is included a new default.css file to add more editor options.

Rumor has it that this mod may be included as a standard feature in an upcoming Y2.2.2 release.