OVerlays:

		new Navstack({
			el: '#foo',
			nav: '.top-nav',
			navItems: {
				fade: '.back-button',
				slide: '.center'
			}
		});

    <div class="top-nav" ns-nav="top">
		  <div class="back-button" ns-transition="fade">
			</div>
		  <div class="center" ns-transition="slide">
			</div>
		</div>