get set css variables code example

Example 1: 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");

Example 2: create variable in css

:root {
  --tab-count: 5;
}

#div1 {
  width: calc(100% - var(--tab-count));
}