declaring css values in variables using js code example

Example 1: how to change css variable in javascript

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

Example 2: set css variable from javascript

document.documentElement.style.cssText = "--tab-count: 3";
/or/
document.documentElement.style.setProperty("--tab-count", 5);
/or/
document.documentElement.setAttribute("style", "--tab-count: 5");