Background Gradient with animated Hue on JavaScript

script.js

function changeBackground() {
	//change color every frame
	//initialise colors ( hue, lightness)
	var hue = 360;
	var light = 0;

	function changeHue() {
		var col1 = Math.abs((hue % 720) - 360);
		var col2 = Math.abs( ( (hue+90) % 720) - 360);
		hue++ ;

  	//values for light adjustment not used
		var light1 = Math.abs( (light % 40) - 20)+60; 
		var light2 = Math.abs( ( (light+10) % 40) - 20)+60;
		light++ ;

		document.body.style.background = 'linear-gradient(to right, hsl('+col1 +',70%, 75%) 0%,hsl('+col2 +',90%,75%) 100%)';
	}
		setInterval	(changeHue, 64);
}
changeBackground();