[TASK] Make buttons context aware

We are dropping the Bootstrap CSS definitions for
buttons to have more control about the styling of
the buttons. From now on we are shipping custom
css adapted to our needs. The new button styling
is context aware and adapts to light and dark
color schemes.

Resolves: #104350
Releases: main
Change-Id: Id6a08557d6414f08cb213420db2a60e70ff4be08
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/85150


Reviewed-by: Benjamin Franzke <ben@bnf.dev>
Tested-by: Benjamin Kott <benjamin.kott@outlook.com>
Tested-by: Benjamin Franzke <ben@bnf.dev>
Tested-by: Andreas Kienast <a.fernandez@scripting-base.de>
Reviewed-by: Andreas Kienast <a.fernandez@scripting-base.de>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Benjamin Kott <benjamin.kott@outlook.com>