Help with a text in start discussion, wrong color

Hi,
I have an issue and is this one:

On https://community.peopleinside.it/ the button to start a discussion has the white text, correct.

If I load a different tag page like https://community.peopleinside.it/t/discussioni the button text is black.
How can avoid this? Any idea of what can cause this or how to find in my CSS?

I was thinking at an issue with the extension Night mode but the issue seems present also with the extension disabled.

Thanks