There are lots of excelent free resources for getting started in HTML here are a few places that I like to go:
The Odin Project:
This site has a pretty decent curriculum for getting started as a web developer
URL: https://www.theodinproject.com/
Codepen.io
This Site is a sandox for testing out single features that you might want to and and should allow you to mess around witht the CSS/JS without having to spin up a full app or pay for hosting
URL: https://codepen.io/