Problem with thumbnail when creating new page

I cordially greet you all.
About two weeks ago, I started a thread here with a problem that has not been solved to date, so I try again.

The problem is that the preview image in the header beats with the image in the “header image” or: if I add “header image” it is everything as it should be, but if I add a preview image to it, both images are over each other and so that it does not a little bit so the preview image doesn’t even stretch across the entire Header to the width as it should be and it expands to the height as it should no longer be. I’m not a professional or I’m a beginner but I think the mistake will be somewhere in CSS. In the comments I will try to explain more …
Anyway, I would be extremely grateful if there was someone who would finally solve my problem and I could use my template for which I paid 100%, thank you