#back_top 
{
	z-index:150;
	position:fixed;
    right:60px;
    bottom:120px;    
}

#back_top a 
{
	z-index: 5;
	position: absolute;
	right: 0;
    height:80px;
    width: 80px;
    opacity: 0.5;
	border-radius: 10px 10px 10px 10px;
	background:url(images/sprite_bignav.png) no-repeat scroll 0 -80px transparent;    
}

#back_top a:hover 
{
	opacity:1;
	background-position: 0 -80px;	
}