function get_randomCssNum()
{
	var ranCssNum= Math.floor(Math.random()*4);
	//var ranCssNum= Math.floor(Math.random()*Number of CSS you Have);
	return ranCssNum;
}

function getaCss()
{
	var whichCss=get_randomCssNum();

	var cssName=new Array(4)
	// var cssName=new Array(Number of CSS you Have)
	cssName[0]="<link rel='stylesheet' type='text/css' href='/css/jan-ligthart-groen.css' media='screen'>";
	cssName[1]="<link rel='stylesheet' type='text/css' href='/css/jan-ligthart-geel.css' media='screen'>";
	cssName[2]="<link rel='stylesheet' type='text/css' href='/css/jan-ligthart-blauw.css' media='screen'>";
	cssName[3]="<link rel='stylesheet' type='text/css' href='/css/jan-ligthart-rood.css' media='screen'>";
	//I am using 5 CSS files in this example. you can add or remove ;)
	//for Add more CSS just add line like this
	//cssName[Next Number]="<link rel='stylesheet' type='text/css' href='CSS FILE URL'>";

	return cssName[whichCss]
}
document.write(getaCss());