Came here to say the same thing. I learned by looking at the source of every other website, before there was minimization, obfuscation, or anything else preventing one from seeing the entirety of the sites code. A few books and websites definitely helped as well.

I used to hit "save as HTML" in IE because I didn't know how favorites worked, and I was afraid of messing up my dad's computer. When I found out that the HTML files could be opened in Notepad, the curtain had been pulled back revealing the secret inner workings, and I was hooked.

My middle school computer club was basically a book group for raw HTML files. We started messing around to see what we could get it to do, but it was mostly feeling around in the dark. I didn't learn about documentation until getting into QBASIC a few years later.