*{padding:0; margin:0;}
.block{
	height:100px; 
	border:3px solid black;
	}
#wrapper {
	margin:auto;
	width:500px;
	height:100px;
	border: 1px solid black;
}
#yellow{
	background-color:yellow;
	width:200px;
	position:absolute;
	left:0px;
	top:0px;
	}
#red{
	background-color:red;
	width:200px;
	position:absolute;
	top:0px;
	right:0px;
	}
#green{
	background-color:green;
	position:absolute;
	left:0px;
	bottom:0px;
	width:200px;
	}
#blue{
	background-color:blue;
	position:absolute;
	width:200px;
	bottom:0px;
	right:0px;
	}