Dead centre a div

centerdiv.css

body 
	{
	margin: 0px
	}

#horizon        
	{
	color: white;
	background-color: #0ff;
	text-align: center;
	position: absolute;
	top: 50%;
	left: 0px;
	width: 100%;
	height: 1px;
	overflow: visible;
	visibility: visible;
	display: block
	}

#content    
	{
	position: absolute;
	left: 50%;
	width: 250px; /* Overall width of div */
	height: 70px; /* Overall height of div */
	top: -35px; /* half of the overall height */
        margin-left: -125px; /* half of the overall width */
        visibility: visible
	}