A CodePen by Hakim El Hattab. Avgrund - A modal concept with a visible level of depth between the page and modal layers.

index.html

<article class="avgrund-contents">
  <h1>Avgrund</h1>
  <p>
		A modal concept with a visible level of depth between the page and modal layers. Click a button below to give it a try.
	</p>
	<button onclick="avgrund.activate( 'stack' );">Stack it</button>
	<button onclick="avgrund.activate();">Grow it</button>
	<p>
		Uses CSS transforms to scale components and CSS filters to blur the page.
	</p>
	<p>
		<em>Avgrund</em> is Swedish for abyss.
	</p>
</article>

<div class="avgrund-cover"></div>

<aside class="avgrund-popup">
	<h2>That's all, folks</h2>
	<p>
		You can hit ESC or click outside to close the modal. Give it a go to see the reverse transition.
	</p>
	<button onclick="avgrund.deactivate();">Close</button>
</aside>

script.js

(function(){

  var container = document.documentElement,
		popup = document.querySelector( '.avgrund-popup' ),
		cover = document.querySelector( '.avgrund-cover' ),
		currentState = null;

  addClass( container, 'avgrund-ready' );

	// Deactivate on ESC
	function onDocumentKeyUp( event ) {
		if( event.keyCode === 27 ) {
			deactivate();
		}
	}

	// Deactivate on click outside
	function onDocumentClick( event ) {
		if( event.target === cover ) {
			deactivate();
		}
	}

	function activate( state ) {
		document.addEventListener( 'keyup', onDocumentKeyUp, false );
		document.addEventListener( 'click', onDocumentClick, false );

		removeClass( popup, currentState );
		addClass( popup, 'no-transition' );
		addClass( popup, state );

		setTimeout( function() {
			removeClass( popup, 'no-transition' );
			addClass( container, 'avgrund-active' );
		}, 0 );

		currentState = state;
	}

	function deactivate() {
		document.removeEventListener( 'keyup', onDocumentKeyUp, false );
		document.removeEventListener( 'click', onDocumentClick, false );

		removeClass( container, 'avgrund-active' );
	}

	function disableBlur() {
		addClass( document.documentElement, 'no-blur' );
	}

	function addClass( element, name ) {
		element.className = element.className.replace( /\s+$/gi, '' ) + ' ' + name;
	}

	function removeClass( element, name ) {
		element.className = element.className.replace( name, '' );
	}

	window.avgrund = {
		activate: activate,
		deactivate: deactivate,
		disableBlur: disableBlur
	}

})();

style.css

* {
  margin: 0;
	padding: 0;
}

html, 
body {
	height: 100%;
	overflow: hidden;
}

html {
	background-color: #222;
	background-image: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAQAAAAECAYAAACp8Z5+AAAAGklEQVQIW2NkYGD4D8SMQAwGcAY2AbBKDBUAVuYCBQPd34sAAAAASUVORK5CYII=);
	background-repeat: repeat;
}

h1, 
h2 {
	font-size: 24px;
}

p {
	margin: 10px 0 10px 0;
	font-size: 16px;
	line-height: 1.32;
}

a {
	color: #7aa76d;
	text-decoration: none;

	-webkit-transition: 0.15s color ease;
	   -moz-transition: 0.15s color ease;
	    -ms-transition: 0.15s color ease;
	     -o-transition: 0.15s color ease;
	        transition: 0.15s color ease;
}
	a:hover {
		color: #91cd85;
	}

small {
	display: block;
	margin-top: 15px;
	padding-top: 15px;
	color: #333;
	font-size: 0.85em;
	border-top: 1px dashed #ccc;

	-webkit-text-size-adjust: none;
}

button {
	border: 0px;
	padding: 8px 10px;
	margin: 5px 0px;
	border-radius: 1px;

	cursor: pointer;
	color: #fff;
	background: #7aa76d;
	font-size: 15px;

	-webkit-transition: 0.15s background ease;
	   -moz-transition: 0.15s background ease;
	    -ms-transition: 0.15s background ease;
	     -o-transition: 0.15s background ease;
	        transition: 0.15s background ease;
}
	button:hover {
		background: #91cd85;
	}
	button:active {
		background: #60895a;
	}
	button+button {
		margin-left: 5px;
	}

.sharing {
	margin-top: 50px;
}

body {
	background: #fff;

	font-family: 'Lato', Helvetica, sans-serif;
	font-size: 16px;
	color: #222;
}
	.avgrund-active body {
		-webkit-transform: scale( 0.9 );
		   -moz-transform: scale( 0.9 );
		    -ms-transform: scale( 0.9 );
		     -o-transform: scale( 0.9 );
		        transform: scale( 0.9 );
	}

.avgrund-cover {
	position: absolute;
	width: 100%;
	height: 100%;
	top: 0;
	left: 0;
	z-index: 1;
	visibility: hidden;
	opacity: 0;
	background: rgba( 0, 0, 0, 0.5 );
}
	.avgrund-active .avgrund-cover {
		visibility: visible;
		opacity: 1;
	}

.avgrund-contents {
	position: relative;
	padding: 20px;
	max-width: 400px;
	height: 100%;
	margin: auto;
}
	.avgrund-active .avgrund-contents {
		-webkit-filter: blur(2px);
		   -moz-filter: blur(2px);
		    -ms-filter: blur(2px);
		     -o-filter: blur(2px);
		        filter: blur(2px);
	}
	.no-blur.avgrund-active .avgrund-contents {
		-webkit-filter: none;
		   -moz-filter: none;
		    -ms-filter: none;
		     -o-filter: none;
		        filter: none;
	}

.avgrund-popup {
	position: absolute;
	width: 340px;
	height: 130px;
	left: 50%;
	top: 50%;
	margin: -130px 0 0 -190px;
	visibility: hidden;
	opacity: 0;
	z-index: 2;
	padding: 20px;

	background: white;
	box-shadow: 0px 0px 20px rgba( 0, 0, 0, 0.6 );
	border-radius: 3px;

	-webkit-transform: scale( 0.8 );
	   -moz-transform: scale( 0.8 );
	    -ms-transform: scale( 0.8 );
	     -o-transform: scale( 0.8 );
	        transform: scale( 0.8 );
}
	.avgrund-active .avgrund-popup {
		visibility: visible;
		opacity: 1;

		-webkit-transform: scale( 1.1 );
		   -moz-transform: scale( 1.1 );
		    -ms-transform: scale( 1.1 );
		     -o-transform: scale( 1.1 );
		        transform: scale( 1.1 );
	}
	.avgrund-popup.stack {
		-webkit-transform: scale( 1.5 );
		   -moz-transform: scale( 1.5 );
		    -ms-transform: scale( 1.5 );
		     -o-transform: scale( 1.5 );
		        transform: scale( 1.5 );
	}
	.avgrund-active .avgrund-popup.stack {
		-webkit-transform: scale( 1.1 );
		   -moz-transform: scale( 1.1 );
		    -ms-transform: scale( 1.1 );
		     -o-transform: scale( 1.1 );
		        transform: scale( 1.1 );
	}


.avgrund-ready body,
.avgrund-ready .avgrund-contents,
.avgrund-ready .avgrund-popup,
.avgrund-ready .avgrund-cover {
	-webkit-transform-origin: 50% 50%;
	   -moz-transform-origin: 50% 50%;
	    -ms-transform-origin: 50% 50%;
	     -o-transform-origin: 50% 50%;
	        transform-origin: 50% 50%;

	-webkit-transition: 0.3s all cubic-bezier(0.250, 0.460, 0.450, 0.940);
	   -moz-transition: 0.3s all cubic-bezier(0.250, 0.460, 0.450, 0.940);
	    -ms-transition: 0.3s all cubic-bezier(0.250, 0.460, 0.450, 0.940);
	     -o-transition: 0.3s all cubic-bezier(0.250, 0.460, 0.450, 0.940);
	        transition: 0.3s all cubic-bezier(0.250, 0.460, 0.450, 0.940);
}
.avgrund-ready .avgrund-popup.no-transition {
	-webkit-transition: none;
	   -moz-transition: none;
	    -ms-transition: none;
	     -o-transition: none;
	        transition: none;
}