Hello, @AnimalShop,
Actually, there is a thing which is that if you change the paragraph font size from the theme options “typography” it will work on complete site paragraph text but if you want to set the product tabs paragraph text size only then you have to make it with the custom CSS code.
You can add the custom CSS code in the XSTRE >> Theme options >> Theme Custom CSS >> Global CSS. Below is the code of it.
.tabs .tab-content p{font-size:12px !important;}
Look at this picture for the code and its results: https://postimg.cc/ygpm4wwm
Note: if you think that I still don’t get your point then please elaborate on it in detail if possible make a video of the issue for a better reference to understand.
Regards 8Themes Team.