Sorry, did you read, what I wrote?
I build the structure for myself. It was not big, but I made a new section, a row with 2 columns and 2 haeding elements. That's it. It looks, like I need it.
The predefined element (Hero 4) I deleted of course, as soon I saw, that both looks identical in backend and frontend editor but NOT in the live view. Only my own made one looks identical.
For me, you can close my question in the forum, because I figured it out for myself. I just wanted to mention for others: If you have these problems, it could be the predefined element.