Why does CSS work with fake elements?

Question

In my class, I was playing around and found out that CSS works with made-up elements.

Example:

Answer 1

Made-up tags are hardly ever used, because it's unlikely that they will work reliably in every current browser, and every future browser.

A browser has to parse the HTML code into elements that it knows, to made-up tags will be converted into something else to fit in the document object model (DOM). As the web standards doesn't cover how to handle everyting that is outside of the standards, web browsers tend to handle non-standars code in different ways.

Web development is tricky enough with a bunch of different browsers that have their own quirks, without adding another element of uncertainty. The best bet it to stick with things that are actually in the standards, that is what the browser vendors try to follow, so that has the best chance to actually work.