I would strongly recommend reviewing your 101 WRT what you're calling tags and clarifying that tags represent elements that are interpreted and rendered by the browser. (The browser does not render tags.)

Also, the distinction of semantics and styling should be cleared up a little. Less emphasis on how elements are styled by default, and more on what they represent.

I like the approach of assuming no knowledge, but this requires extra care to introduce concepts without using improper or misleading terminology. As a beginner, there's not much worse than hearing simplifications and thinking they're the whole story.

Good luck with continuing your series!