[BUGFIX] News Box in BE Login Screen not styled properly

The headline in the backend login screen that contains
the sys_news information has a bottom margin and
does not have the right size.

Releases: 6.2
Resolves: #58362
Change-Id: I0977a3be627a469b902fb39b14417dc9feb738da
Reviewed-on: https://review.typo3.org/29745
Reviewed-by: Nico Schober
Tested-by: Nico Schober
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters