w3.org do report 3 CSS errors on the home page at the moment.
I keep a few browsers on my operating systems to check that my own websites are never browser specific. I tried this site on nine different browsers and found similar problems to those you describe on two of them and one browser which froze.
The browsers that gave problems for me on this site were not popular main stream browsers. (Cyberfox, Midori and Vivaldi)
I could not try any Windows only browsers because I have not got a Windows operating system installed on any of my computers at the moment.