Visually correct vertical centering with Flexbox + margin fallback

dabblet.css

/**
 * Visually correct vertical centering with Flexbox + margin fallback
 * Lea Verou & David Storey
 * Slight adjustment by Vasilis van Gemert
 */

html, body { height: 100%; }

body {
	width: 100%; /* needed for FF */
	height: 90%; /* needed for your eyes */
	margin: 0;
	
	/* Flexbox hawtness */
	display: box; display: flexbox;
	box-align: center; flex-align: center;
	box-pack: center; flex-pack: center;
}

div {
	padding: 1em 1.5em;
	
	/* Fallback to look decent w/out Flexbox */
	max-width: 10em;
	margin: 1em auto;
	
	/* 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"}