Add page background color is missing

Description of problem:

Add page without the light-gray background misses the contrast to understand the grouped boxes.

Prerequisites (if any, like setup, operators/versions):

None

Steps to Reproduce

1. Open developer perspective and open the add page

Actual results:

Boxes has a white background and are shown on a white page background.

Expected results:

Boxes has a white background and should be shown on a light-gray page background.

Reproducibility (Always/Intermittent/Only Once):

Always

Build Details:

Local frontend 4.9 Master (tested with 6b93a169805ac6b4e5f477bd41ee774359ed2275)

Additional info: