different post theme file for different categorys

Hi there im new to this so im probably asking very simple questions. Is there a simple way to change the post theme file depending on what page you are viewing it from. I.e.

this page has a certain post theme
https://www.jonathantopf.com/test/?cat=3

and this also has a diferent post theme
https://www.jonathantopf.com/test/?cat=7