I would definitely go for w3schools.com, they have very helpful guides for HTML and CSS and lots of different languages and it teaches you different aspects and features of them, and best of all its totally free!
on YouTube there are hundreds of different tutorial videos out there for HTML and CSS, my go to channels would be Programming with Mosh, Fireship, Brocode and freecodecamp.org (that's their full username im not linking their website).
Hope this helps!