[TASK] Adjust collapse page tree button

To make the collapse page tree button more visible and usable
for BE User the button size needed to be increased.

Resolves: #65930
Releases: master
Change-Id: I3ee6b9036d7152f04ab49fd82d5cd3d79af93b4c
Reviewed-on: http://review.typo3.org/38077


Reviewed-by: Benjamin Kott <info@bk2k.info>
Tested-by: Benjamin Kott <info@bk2k.info>
Reviewed-by: Andreas Fernandez <andreas.fernandez@aspedia.de>
Tested-by: Andreas Fernandez <andreas.fernandez@aspedia.de>
Reviewed-by: Benjamin Mack <benni@typo3.org>
Tested-by: Benjamin Mack <benni@typo3.org>