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dabblet.css

#wrapper { 
			width: 900px;
			margin: 0 auto;
			position: relative;
			background: #999;
		}

		#content {
			width: 500px;
			float: right;
			height: 500px;
			background: blue;
		}

		#sidebar-wrap {
			position: relative;
			top: 0;
			left: -300px;
			width: 300px;
			height: 600px;
			background: yellow;
		}

		#sidebar {
			position: fixed;
			top: 0;
			margin-left: -300px;
			height: 500px;
			width: 300px;
			background: red;
		}

dabblet.html

<div id="wrapper">

	<div id="content"></div>

	<div id="sidebar-wrap">
		<div id="sidebar">
		</div>
	</div>

</div>

settings.json

{"view":"split","seethrough":"","prefixfree":"1","page":"css"}