[BUGFIX] Improve / Modernize style for preview notice

Resolves: #38735
Releases: master
Change-Id: I5339f7a031b1e365c1d70c6ccb079bcff827c09e
Reviewed-on: https://review.typo3.org/53558


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Jan Helke <typo3@helke.de>
Tested-by: Jan Helke <typo3@helke.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>