d = document;
window.onload = function() {
	altColors();

}

function altColors() {
	var systems = d.getElementById('main');
	var divs = systems.getElementsByTagName('div');
	alt = true;
	for (i=0; i<divs.length; i++) {
		if (divs[i].className == 'product'){
		
		if (alt == true) { divs[i].className = 'product alt'; alt = false;
		
		} else {alt = true;}
		
		
		}
	}
}