@yoizfefisch Very nice! 
All of the fCC tests pass, I don’t see any errors or warnings in the HTML, CSS, or WAVE (accessibility) validation tools. I don’t see any ID selectors in the CSS, nor any inline CSS. I don’t see overqualified CSS selectors. The form mostly looks and works well on smaller and larger viewports widths. All in all, you’ve done really well here! 
One thing I notice that you might want to work on is that the textarea box shrinks too much for smaller viewport widths, at least in the responsive design mode for Firefox and Chrome:
Firefox
Chrome
I recently found this helpful tool to help visualize what a site looks like on different viewport widths: Material.io Resizer. It’s basically the same as the browser’s responsive design mode, but it’s a slightly more visual way to see how a site renders.
The textarea issue is the only issue that stood out to me. Great work! 
@camper Thanks for your feedback. I fixed the textarea by adding min-width .