isa666

Thanks! Now it appears as clean also on my checker. I cleared the cache before, so it should have worked before.

I just solved it:

I used a custom CSS plugin and added the code displayed in the question here. That works.
I have no idea why it does not work in the “custom CSS” section in the WordPress customizer.

But anyway, thanks for the link! Might be useful next time.

Thank you so much! There is indeed a typo in the link.
Please check here:
https://www.yogaundkrautgefluester.de/ueber-mich

I now made a point without space afterwards. This works. There is also no problem with commata or any other punctuation mark.