David, thank you for your additions and your explanations. I am at a loss with regard to your container block [#A] and [#B] explanations. In my opinion, this is exactly how I do it.
Global setting: ELEMENTS > Layout > Full width
2) inner container
If I insert your code @media …, I still have the problem that in the tablet and mobile view the background colour cannot be displayed borderless on the left and right due to the padding.
Would you please be so kind and create a page / post in the cms backend or edit the testpage (all is still in dev mode) with the parameters that it needs from your point of view? Feel free to play around …