Issue with Jupyterthemes - Only applies on the output

Hi, I have recently changed laptops and I am struggling to apply jupyter themes properly - for some reason the theme only applies on the output rather than on the full screen.
I tried everything I could think of - from installing/uninstalling into different paths due to admin rights etc, changing browsers, using conda install conda-forge::jupyterthemes as well as pip… and nothing seems to be helping. I have never had this issue previously and I am unsure what else I could try, would really appreciate if someone could help out. Thank you!