change a css variable with javascript code example

Example 1: javascript get css variable

let docStyle = getComputedStyle(document.documentElement);

//get variable
let myVarVal docStyle.getPropertyValue('--my-variable-name');

//set variable
docStyle.setProperty('--my-variable-name', '#fff');

Example 2: how to change css variable in javascript

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