buffet.scss: consolidate .LayoutSideMenu
buffet.scss: consolidate .LayoutSideMenu

The use of colors is pretty much incompatible between this
theme and the default theme, so for now I don't see other
option than just leaving the colors and fonts here.

https://phabricator.endlessm.com/T11949

endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib