How to control Sass Variable with javascript

Question

I have a Sass file which is generating a CSS file. I have used many variables in my sass file for background color, font-size, now I want to control my all variables through

Answer 1

variable in style

:root {

  --bg: #000;
  --font-size:12px;

}

change variable value by javascript

root.style.setProperty('--bg', '#fff');
root.style.setProperty('--font-size', '14px');