I was thinking that it's so weird to talk about using standard HTML validation and then everything is shown with React? If we want to teach people how standard works, we can't assume React as the default.
While that link is great advice it's not 100% true that you need to have JS enabled to render anything in a web component - there's declarative shadow dom. Also while it's also true to depend on as little as possible JavaScript it's also required for some accessibility aspects. You can get far with only HTML and CSS but not always all the way.