If you open devtools and change the value a css variable (other examples: change from a breakpoint or :hover... or anything else), this change happens in realtime, JavaScript is unable to detect this ...

Update-Css-Variable Update CSS Variables with JavaScript This project demonstrates how to use JavaScript to update CSS variables, also known as custom properties.

Web designers use CSS to turn basic HTML into cutting-edge visual layouts. Our getting-started guide tells you everything you need to know to understand it.