bug#54196: 29.0.50; flat-button face box style does not work as expected

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: da_vid@orange.fr,  54196@debbugs.gnu.org
> Date: Mon, 28 Feb 2022 13:57:02 +0100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Strangely enough, I don't see any difference in behavior before and
> > after the change.
> 
> Did you test with the :color before the :style?

I've used the code you posted.  It behaved correctly (AFAIU) for me
even before the change, and it continues to behave correctly after the
change.