Apples and oranges.
CSS is what you use to “style” elements on the page.
JS is a scripting “language” used extensively for web applications
HTML is what is used (along with CSS) to build web pages
I would suggest that you Google a little to gain some perspective on each.
Most of the time using RW, you won’t need to do much with JS or HTML on your own as the basic functionality is already in place in the themes or available via already written stacks.
CSS is helpful though to “tweak” the styling to get what you want.