Changing CSS pseudo-element styles via JavaScript

Question

This question already has answers here:

Answer 1

If you're comfortable with some graceful degradation in older browsers you can use CSS Vars. Definitely the easiest of the methods I've seen here and elsewhere.

So in your CSS you can write:

#editor {
  --scrollbar-background: #ccc;
}

#editor::-webkit-scrollbar-thumb:vertical {
  /* Fallback */
  background-color: #ccc;
  /* Dynamic value */
  background-color: var(--scrollbar-background);
}

Then in your JS you can manipulate that value on the #editor element:

document.getElementById("#editor").style.setProperty('--scrollbar-background', localStorage.getItem("Color"));

Lots of other examples of manipulating CSS vars with JS here: https://eager.io/blog/communicating-between-javascript-and-css-with-css-variables/