[BUGFIX] EXT:form - Bring back missing default CSS styles

Re-add the default CSS styles for EXT:form.
The default CSS styles have been removed by accident during the rewrite.

Resolves: #72863
Releases: master, 7.6
Change-Id: Id03771f37674f3cb5e678a9a2d5585880501cd35
Reviewed-on: https://review.typo3.org/46149


Reviewed-by: Bjoern Jacob <bjoern.jacob@tritum.de>
Tested-by: Bjoern Jacob <bjoern.jacob@tritum.de>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Reviewed-by: Frank Nägler <frank.naegler@typo3.org>
Tested-by: Frank Nägler <frank.naegler@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>