Almost every repl I make does not run
that often happens, and also today at about 10:30am ish repl.it was down and everything was being slow and you couldnt access notifications and it wasnt loading; basically the site wasn't working. So maybe thats why your repl isnt working, but you also say that every HTML/CSS/JS repl you make has the same error, so maybe it isnt due to repl.it being down. Besides, that outage is fixed now, so if its still not working for you then its a different problem.
Yeah, that happened to me before a while ago. I ended up leaving it and the next day it worked fine. I think that repl.it is currently experiencing some issues because there are a lot of people asking about this sort of thing. Just report it as a bug and then wait (try a different browser as well, sometimes that helps)