document.documentElement.setAttribute("style", "--main-background-color: green");
document.documentElement.style.setProperty("--main-background-color", "green");
let root = document.documentElement;
root.addEventListener("mousemove", e => {
root.style.setProperty('--mouse-x', e.clientX + "px");
root.style.setProperty('--mouse-y', e.clientY + "px");
});