Lol ... my nickname is Buelipix, not Buelepix ;-))

What is the function of light gray margins added?

The picture is only a draft, not the finished advertisement. The two light gray borders are only added so that the mock-up can be inserted into an ipernity article as a medium format. Because unfortunately the medium setting does not work in our editor.
So it is so to say a private work-around for the existing editor bug.