how to put a color variable from js to css code example

Example 1: how to change css variable in javascript

document.documentElement.setAttribute("style", "--main-background-color: green");

Example 2: css variables

:root {
  --background-color: #333;
  --text-color: #fff;
}
body {
  background-color: var(--background-color);
  color: var(--text-color);
}