It's great that you confirm it works fine on mac.
I had a chance to test it on windows.
It seems this is a problem caused by OpenSees 3.1 windows version, at least one material is not working.
We're rebuilding OpenSees and will let you know if it works.
Thanks for pointing out the dark mode appearance.
I seldom use dark mode, so never noticed that, until you pointed it out.
I'll see what I can do about it.