fix: Classic skin: Some rules depend on @window-background having an actual value

(integrated from komodo (trunk) change 82549 by nathanr)

git-svn-id: https://svn.openkomodo.com/repos/openkomodo/trunk/src/modules/classic_skin@13831 b87d16e7-d29f-4ee1-b5ec-817d645d335f
fix: Classic skin: Reset tab styling

(integrated from komodo (trunk) change 82552 by nathanr)

git-svn-id: https://svn.openkomodo.com/repos/openkomodo/trunk/src/modules/classic_skin@13834 b87d16e7-d29f-4ee1-b5ec-817d645d335f