I've always preferred square avatars, especially when a square image is rounded and parts of the image are cut off.
How can I force avatars to be square in all forum styles? I've seen custom CSS code to force round, but my attempts to force square have failed.
I used Chrome's style checker and found all the places (so far) that were forcing rounded avatars. Things are looking much better now, IMHO.
I entered all the custom CSS into WP's Appearance>Customize>Additional CSS. Worked very well. Hopefully the changes are safe from future updates. And hopefully this post might help someone else.
For anyone interested, the key item to look for is "border-radius". For rounded, the value will be 50%. I changed them to 0 (not 0%, just 0). My site is Infinite Realities if you'd like to see.