[BUGFIX] Workspaces: Fix broken buttons in frontend

Adds a font size to the button text, so the button text in the
"send stage" windows in the workspace dialogs used in the
frontend become visible again. Also, a background color is
added to the top buttons to fix the "cut".

Resolves: #65102
Releases: master, 6.2
Change-Id: I928299e602829b322e3c6515367bcf1ac59b2479
Reviewed-on: http://review.typo3.org/37097


Reviewed-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Tested-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Reviewed-by: Nicole Cordes <typo3@cordes.co>
Reviewed-by: Frederic Gaus <gaus@flagbit.de>
Tested-by: Frederic Gaus <gaus@flagbit.de>
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>