function getPageHeight(){
	var body = document.body,
		html = document.documentElement;

	var height = Math.max( body.scrollHeight, body.offsetHeight, 
		html.clientHeight, html.scrollHeight, html.offsetHeight );

	var overlay = document.getElementById('backdrop'); 
	
	overlay.style.height = height + 'px'
}

function hide_div(div_name){
		//document.getElementById(div_name).className='none'
		$('#'+div_name).removeClass('block').addClass('none');
}

function show_div(div_name){
		//document.getElementById(div_name).className='block'
		$('#'+div_name).removeClass('none').addClass('block');
}