[BUGFIX] Fix dark mode styling of systemwide settings

Resolves: #104968
Releases: main
Change-Id: I0ca52db1b2b7ba3162f334c35242cce2b4424211
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/86103


Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Guido Schmechel <guido.schmechel@brandung.de>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Guido Schmechel <guido.schmechel@brandung.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>