Theory and readings

Good day guys.
as a new user i just have a question, i have noticed that the curriculum is practical based isn’t there a platform where a new user coder can learn theory to supplement the practical as i am still learning html and basic css

every new thing you learn you can read more about it on the documentation, for example on the MDN (Mozilla Developers Network) https://developer.mozilla.org/

or do you want a book or something?