How to Get Circular Avatar Images in WordPress

I don’t know if I can ask you this kind of question… I need some help with my User profile design. I want my user to have this circular profile image design. I have all the steeps to do that from here:

Its seem, easy. I followed it steep by steep (Appearance > Editor > Stylesheet – style.css and past the code) but I don’t see the result. My profil still in square forme.
Can you help me?

Thank you again for your help and advices.