[TASK] Give install tool a fresher look

[TASK] Give install tool a fresher look

During the last-minute changes before LTS, some stylings in the
Maintenance area were done to streamline the look&feel, but the
installer process should get an update look as well.

Resolves: #86756
Releases: master
Change-Id: Idb58da1f467c27ce3e12252f201e031c2faaedc2
Reviewed-on: https://review.typo3.org/58543
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>