how to change css variable in javascript

JavaScript
let docStyle = getComputedStyle(document.documentElement);

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

//set variable
docStyle.setProperty('--my-variable-name', '#fff');document.documentElement.setAttribute("style", "--main-background-color: green");document.documentElement.style.setProperty("--main-background-color", "green");document.documentElement.style.cssText = "--main-background-color: red";
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