Hi Leo,
thanks for the quick reply.
I investigated your point and I found that … I am dumb: before setting up that manual G Suite creative that I am displaying now, my Google Ad Manager account was falling back to AdSense (configured so to cover for when I don’t have a campaign) who in turn was serving a fixed 320×50.
Since the AdSense ad was a fixed size and not automatically centered, I was experimenting with the CSS to force it centered. When I finally got that GSuite fluid native creative, I forgot about the experimentation and the relative CSS code. ๐
Thank you very much.