Answer 1

You can use JavaScript to change CSS values indirectly through CSS variables.
https://code.sololearn.com/Wa725Y80c5ps/?ref=app

Answer 2

Yes it's possible but not possible in css file.
You can get the element(s) and use javascript to change the style

Answer 3

You can't call JS variables into css file because css is not a programming language It is just a style sheet language.
A better question is: what you are trying to do? let us help you!

Answer 4

As Simple As This:
var bg='blue';
element.style.backgroundColor=bg;