[BUGFIX] Make element tree styles more explicit

A display bug of the element tree component is
resolved by making the css definition more explicit,
overwriting globally defined styles.

Resolves: #99630
Related: #97036
Releases: main
Change-Id: Ia040795fb9f784abee26743235d410d45f3c2be1
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77488


Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Frank Nägler <frank.naegler@typo3.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Frank Nägler <frank.naegler@typo3.com>