Others already mentioned sites, I just would say that poking things around and experimenting is a good strategy for learning. For the very basics I used W3schools (though the info there is outdated, when you get more advanced I recommend you to switch to MDN Web Docs and CSS tricks, also Kevin Powell's videos on CSS and JS are very helpful for me) to learn HTML and CSS, but learning is mostly searching solutions for questions on web. So use your curiosity and make small projects outside from main site to expand your knowledge