I'm pretty new to CSS and have no idea how to describe this problem to find a solution

https://preview.redd.it/6n9bux7x9w4g1.png?width=1594&format=png&auto=webp&s=fc2e01d77fca1ea92b8e6eb70cf2671f17410faa

What it says on the tin, I don't know how to word what this is to find resources to figure out what's wrong and was wondering if anyone had experience with this issue. Whenever I select body text it does... That. I can paste my stylesheet if that would help, but it might have to be in the comments because Reddit is throwing errors at me when I try to paste it here.