[BUGFIX] Ensure scrollbar styling is evaluated for each element

The CSS property `--typo3-text-color-base` is changed on a per-element
basis (e.g. with the class mode theme) and therefore the scrollbar
style needs to applied based on the current value of this variable.

Resolves: #105223
Releases: main
Change-Id: Ib9e6dbd4339ae2f454eef7daf44c8e62a599c682
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/86454


Tested-by: Benjamin Franzke <ben@bnf.dev>
Tested-by: Andreas Kienast <akienast@scripting-base.de>
Reviewed-by: Andreas Kienast <akienast@scripting-base.de>
Reviewed-by: Benjamin Franzke <ben@bnf.dev>
Tested-by: core-ci <typo3@b13.com>