outer DIV to 100%

dabblet.css

/**
 * outer DIV to 100%
 */

html * { font-size:100%; }
body {
	padding: 0;
	margin: 0;
	font-family: Arial, Helvetica, sans-serif;
	font-size: 87.50%;
	-webkit-text-size-adjust: 100%;
	-ms-text-size-adjust: 100%;
}
h1, h2, h3, h4, h5, h6 {
	font-size: 125.00%;
	line-height: 1em;
}

.wrapper {
	width: 960px;
	margin: 0 auto;
}
.wrapper .inner {
	padding: 1em 10px;
}

.header, .main {
	width: 100%;
	margin: 0 0 1em;
	background: rgba(0,0,0,.6);
	color: white;
}
.header {
	display: block;
}
.main {
	display: table;
}

dabblet.html

<div class="header" role="banner">
	<div class="wrapper">
		<div class="inner">
			<h2>1. Versuch</h2>
			<p>div.header ist display:block</p>
		</div>
	</div>
</div>

<div class="main" role="main">
	<div class="wrapper">
		<div class="inner">
			<h2>2. Versuch</h2>
			<p>div.header ist display:table</p>
		</div>
	</div>
</div>

settings.json

{"view":"split","fontsize":"100","seethrough":"","prefixfree":"1","page":"css"}