HTML is pretty straightforward so just understanding the very basic stuff is probably all you need. CSS is where html gets any challenge it might have.

CSS is weird because it's very "easy" so "real developers" kind of object to learning it, but the truth is, if you gave any of them a layout design, they probably couldn't build it. There are tools like tailwind to help, but, IMO, tailwind just helps you avoid learning css's vocabulary, but you just replace it with having to learn tailwind's vocabulary.

JavaScript on the other hand is a "real" programming language, though decidedly quick-n-dirtier than other languages. It lets you be a lot more sloppy. (Tbh it's a lot more forgiving than css!). As a result, it lacks the elegance and control that "real developers" like -- and, as most people's first language, it lets newcomers get into bad habits. For these reasons, JavaScript is a bit derided -- but, unlike CSS, most developers can't avoid it.

There are a few key ideas in JavaScript that, once you understand them, things make a lot more sense. (I won't get into them now, since it doesn't sound like you're at the point where that kind of clarity would help, but, when you are, come on back here and make a post!)

TLDR: HTML is definitely something you can just pick up along the way. JavaScript is a real language that will take a little while to feel comfortable with, and it will take a career to master. CSS will never be easy, so don't let it hold you back.

Assuming the project uses them, yes. Might want to check with the project owner to be sure before jumping in.

This course is good

Mozilla has good introduction guides into web development https://developer.mozilla.org/en-US/docs/Learn