var mainNav= document.getElementById("mainNav");
var li= mainNav.getElementsByTagName("li");

for(i=0; i<li.length; i++){
	li[i].ids = i;
	
li[i].onmouseover = function(){
		var m=this.ids;
		if(li[m].className=="now" ){
		li[m].className = "now over";}else{
		li[m].className = "over"
		}
}
li[i].onmouseout = function(){
		var m=this.ids;
		if(li[m].className=="now over" ){
		li[m].className = "now";}else{
		li[m].className = ""
		}
}

}