For most basic Dash apps, you really don’t need any JavaScript, React, or even much CSS or HTML. You can do so much with pure Python. If you are getting to this level of detail in such a short time, you are making great progress and doing some quite advanced apps!
AG Grid can do some really cool stuff with just a little bit of JavaScript though. I know I’ve learned a lot in the last year working on the grid. It’s been really fun.
I rely on the MDN Web Docs for most of the JavaScript, CSS and HTML things. React has a fanatic tutorial as well: Quick Start – React.