[TASK] Page module styling

* styling for the BE layout (grid element)

Resolves: #43208
Releases: 6.0

Change-Id: I80637c5fc49b3f612399f4c42d863520b39b008b
Reviewed-on: http://review.typo3.org/16752
Reviewed-by: Steffen Ritter
Tested-by: Steffen Ritter
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel