var root = document.documentElement;
var styles = getComputedStyle(root);

var setFactor = function() {
	var inlineSize = parseFloat(styles.inlineSize);
	var fontSize = parseFloat(styles.fontSize);
	root.style.setProperty('--screen-size', inlineSize / fontSize);
};

window.addEventListener('resize', setFactor);
window.addEventListener('load', setFactor);