bug#45735: Adding a flat-button style for boxes

[Lars Ingebrigtsen]

Pedro Andres Aranda Gutierrez <paaguti@gmail.com> writes:

> Create a flat-button style for boxes. It is based on the simple button
> style but uses the background colour instead of the foreground colour
> for the box.
> This greatly simplifies the extension of Emacs themes to adapt them to
> modern GUIs where the buttons are flat.

Looks good to me, so I've pushed this to Emacs 28 (with added
documentation).

This change was small enough to apply without assigning copyright to the
FSF, but for future patches you want to submit, it might make sense to
get the paperwork started now, so that subsequent patches can be applied
speedily. Would you be willing to sign such paperwork?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no