#main {
	width: 700px;
	margin: 0 auto;
	position: relative;
}
#sidebar {
	width: 170px;
	float: left;
}
#sidebar:before {
	content: " ";
	width: 170px;
	height: 100%;
	background: #c9e4ca;
	position: absolute;
	z-index: -1;
}