Changing CSS pseudo-element styles via JavaScript


Is it possible to change a CSS pseudo-element style via JavaScript?

For example, I want to dynamically set the color of the scrollbar like so:

document.querySelector("#editor::-webkit-scrollbar-thumb:vertical").style.background = localStorage.getItem("Color");

and I also want to be able to tell the scrollbar to hide like so:

document.querySelector("#editor::-webkit-scrollbar").style.visibility = "hidden";

Both of these scripts, however, return:

Uncaught TypeError: Cannot read property 'style' of null

Is there some other way of going about this?
Cross-browser interoperability is not important, I just need it to work in webkit browsers.