You don't need JavaScript.
The reverse isn't true. You can't make a page out of just JavaScript. Even if JS builds your DOM and builds the styles for it (because hey, crazy people have crazy ideas) the DOM and styles are still HTML + CSS. You still need to know what the JS should build.
Not exactly true. Some frameworks (like DHTMLX) allows one to generate forms, pages, images and even complex UI layouts with just code and without a single line of html or css.
Although I concede it's arguable whether or not this still counts as "just javascript," it's still true that, in the end, you wind up with just HTML, either machine generated or human generated.
I'm not saying this is a perfect situation, but the truth is that html and css skills are somewhat less valuable for a web developer nowadays.
Just an example, this UI takes 35 lines of javascript code to be created using DHTMLX:
https://dhtmlx.com/docs/products/visualDesigner/live/?previe...
for those who want to play around:
https://dhtmlx.com/docs/products/visualDesigner/live/#c403w3
A backend programmer.
(Doing big things in JS right now is still asking for trouble.)