HyperText Markup Language is semantic. You're marking up a document to show what information it contains, where it contains it, and how it relates to other documents or information. Reading markup causes browsers to display things, but that's incidental.

In theory.

In practice, no one cares about semantics and the tags are chosen based on how a target set of browsers happens to display them.

Your question about who interprets markup is exactly right. In theory, you have no idea. Maybe it's a browser, maybe it's assistive software, maybe it's a browser printing, maybe it's some custom knowledge base that shows a different view of documents to different users. In theory, you're supporting all of that by only marking up semantics and allowing the consumer to interpret them, because there isn't one right answer.

In practice, your client is Chrome.

In theory, that's irrelevant because you're using CSS to style semantic markup so it works in Chrome and still makes sense to other clients.

In practice, you're writing a web application, using a framework, and nothing in the stack wants you to do that.