.cover_off
{
	display: none;
	position: absolute;
	left: 0px;
	top: 0px;
	width: 0px;
	height: 0px;
	background: transparent;
}
.cover_on
{
	display: block;
	position: fixed;
	left: 0px;
	top: 0px;
	width: 100%;
	height: 100%;
	background: url(images/cover.png);
}