var root = document.querySelector(':root');
root.style.setProperty('--variable', 'lightblue');
/or/
root.style.setProperty('--variable', myColor); let docStyle = getComputedStyle(document.documentElement);
//get variable
let myVarVal docStyle.getPropertyValue('--my-variable-name');
//set variable
docStyle.setProperty('--my-variable-name', '#fff');getComputedStyle(document.documentElement)
.getPropertyValue('--my-variable-name'); // #999999document.documentElement.style.setProperty("--main-background-color", "green");// this is for site-navigation with more sub ul-blocks.
// in css root{--ul-hover-height:100px} //fallbackvalue
// in css: nav ul ul:hover{height:--ul-hover-height;}
// to make it dynamic using JS:
// set variable ul ul height depending on nr. of li's:
function setUlHeight(elem){
parentHeight=window.getComputedStyle(elem.parentNode).height
parentHeight=parseInt(parentHeight)*1.2 //to cover li padding/margin..
elemHeight=parentHeight * elem.childElementCountdocument.documentElement.style.cssText = "--tab-count: 3";
/or/
document.documentElement.style.setProperty("--tab-count", 5);
/or/
document.documentElement.setAttribute("style", "--tab-count: 5");