dabblet.css

/**
 * Vertical centering with inline-block + generated-content
 * Julien Cabanès
 * based on http://css-tricks.com/centering-in-the-unknown/
 */

html, body { height: 100%; }
body {
	display: inline-block;
	margin: 0;
	padding: 0;
	width: 100%;
	text-align: center;

}
body:before {
	display: inline-block;
	content: '';
	height: 100%;
	vertical-align: middle;
}

div {
	display: inline-block;
	vertical-align: middle;
	padding: 1em 1.5em;
	
	/* Fallback to look decent w/out Flexbox */
	max-width: 10em;
	
	/* Make it pretty */
	background: slategray;
	text-align: center;
	border-radius: .3em;
	color: #405060;
	font: bold 150% sans-serif;
	text-shadow: 0 2px 1px hsla(0,0%,100%,.2);
}

dabblet.html

<div>OMG, I’m centered!</div>

settings.json

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