Obviously all sorts of people learn all sorts of ways, but here is my 10c…
As a complete beginner you’ll find a tonne of jargon pretty quickly and the practical application may not be clear from just reading. I’m not familiar with the book you mentioned, but I know the book I learned with had me doing a lot of hands-on stuff straight away anyway. You might find you don’t need to do the HTML/CSS challenges at all in that case! (I didn’t really need to do them, I just liked racking up easy brownie points).
The things I like about the FCC challenges is that you can just start, right now. You don’t need to research and pick an editor to write in, you don’t need to keep refreshing a browser to see changes. And, you get instant feedback on your work. Books are a good resource, but a little too abstract for me as the first port of call for learning to code.
You’ll get better at coding by coding everyday - the reading might help things stick, but diving straight in is the best experience I’ve found.