[BUGFIX] Add background-color to Link Wizard Attribute Container

Background color was added to the Link Wizard Attribute Container,
to fit with the leading tab navigation.

Releases: master, 8.7
Resolves: #81404
Change-Id: Idcc009ec2b02da367a1ed749e3a5c746fed43717
Reviewed-on: https://review.typo3.org/52992


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Mona Muzaffar <mona.muzaffar@gmx.de>
Tested-by: Mona Muzaffar <mona.muzaffar@gmx.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>