#fondo_transparente { position: fixed; left: 0; top: 0; display: none; float: left; width: 100%; height: 100%; background: #000; z-index: 1;
	filter: alpha(opacity=70); /*Explorer*/ opacity: .7; /*Firefox*/ -moz-opacity: 0.70 /* Mozilla*/ }
* html #fondo_transparente { /* ie6 hack */ position: absolute; }