[BUGFIX] Scale images in content element preview

Added CSS to ensure images are contained in parent element.

Resolves: #79971
Releases: master
Change-Id: I38a4038af067166d771d012e2ddc0e2983060513
Reviewed-on: https://review.typo3.org/51802


Reviewed-by: Morten Pless <mpl@systime.dk>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Joerg Boesche <typo3@joergboesche.de>
Reviewed-by: Christer V <cvi@systime.dk>
Reviewed-by: Timo Hund <timo.hund@yahoo.com>
Tested-by: Timo Hund <timo.hund@yahoo.com>
Reviewed-by: Josef Glatz <josef.glatz@typo3.org>
Tested-by: Josef Glatz <josef.glatz@typo3.org>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>