var position = 0;
var color = "none";

function startPolling(){
	setInterval("poll()",500);
}

function poll(){
	if (navigator.appName == "Microsoft Internet Explorer"){
		var position = document.body.scrollTop;
	} else {
		var position = window.pageYOffset;
	}

	if (position > -1  && position < 450){
		switchToOverview();
	}
	
	if (position > 650 && position < 1100){
		switchToDetails();
	}
	
	if (position > 1400 && position < 1950){
		switchToGetInvolved();
	}
	
	if (position > 2000 && position < 2500){
		switchToContact();
	}

	return true;

}

function switchToOverview() {
	changecss('.overview_H','background-position','0 -19px');
	changecss('.details_H','background-position','0 0px');
	changecss('.getInvolved_H','background-position','0 0px');
	changecss('.info_H','background-position','0 0px');
}

function switchToDetails() {
	changecss('.overview_H','background-position','0 0px');
	changecss('.details_H','background-position','0 -19px');
	changecss('.getInvolved_H','background-position','0 0px');
	changecss('.info_H','background-position','0 0px');
}

function switchToGetInvolved() {
	changecss('.overview_H','background-position','0 0px');
	changecss('.details_H','background-position','0 0px');
	changecss('.getInvolved_H','background-position','0 -19px');
	changecss('.info_H','background-position','0 0px');
}

function switchToContact() {
	changecss('.overview_H','background-position','0 0px');
	changecss('.details_H','background-position','0 0px');
	changecss('.getInvolved_H','background-position','0 0px');
	changecss('.info_H','background-position','0 -19px');
}


//onclick="changecss('.exampleA','color','red')"

function changecss(theClass,element,value) {
	//Last Updated on May 21, 2008
	//documentation for this script at
	//http://www.shawnolson.net/a/503/altering-css-class-attributes-with-javascript.html
	 var cssRules;
	 if (document.all) {
	  cssRules = 'rules';
	 }
	 else if (document.getElementById) {
	  cssRules = 'cssRules';
	 }
	 var added = false;
	 for (var S = 0; S < document.styleSheets.length; S++){
	  for (var R = 0; R < document.styleSheets[S][cssRules].length; R++) {
	   if (document.styleSheets[S][cssRules][R].selectorText == theClass) {
	    if(document.styleSheets[S][cssRules][R].style[element]){
	    document.styleSheets[S][cssRules][R].style[element] = value;
	    added=true;
		break;
	    }
	   }
	  }

	  if(!added){
	  if(document.styleSheets[S].insertRule){
			  document.styleSheets[S].insertRule(theClass+' { '+element+': '+value+'; }',document.styleSheets[S][cssRules].length);
			} else if (document.styleSheets[S].addRule) {
				document.styleSheets[S].addRule(theClass,element+': '+value+';');
			}
	  }
	 }
	}