div#col1 {
	float: left;
	width: 160px;
	background: lightblue;
}

div#col2 {
	float: right;
	width: 200px;
	background: burlywood;
}

div#centre {
	background: khaki;
}

div#centre {
	margin-left: 170px;
	margin-right: 210px;
	…
}