Started going through the lesson in https://www.codecademy.com/courses/learn-html/lessons/intro-to-html/exercises/text-content-tags
Everything was fine, I switched to another window, came back and it has been unable to connect ever since.
Win 10, Chrome, AdBlock disabled for this site. Tried incognito mode in Chrome, tried Edge with the same result. Home Wifi network, nothing changed when that happened.