Backend & Frontend View different …background colors gone, wrong image sizes

Hello,

can anybody please help?

I have a fresh WP install, created a simple Elementor Layout which looks good in backend view. But when I look at it frontend view it’s a mess…section background colors are gone, images a completely wrong size, etc.

I already tried a few things without success, like: changing themes, updating elementor, setting checkmarks in elementors settings.