https://www.apex66.co.uk/wp-content/themes/apex22/js/overlay-menu.js

1(function() {
2	var triggerBttn = document.getElementById( 'trigger-overlay' ),
3		overlay = document.querySelector( 'div.overlay' ),
4		closeBttn = overlay.querySelector( '.overlay-close' );
5		transEndEventNames = {
6			'WebkitTransition': 'webkitTransitionEnd',
7			'MozTransition': 'transitionend',
8			'OTransition': 'oTransitionEnd',
9			'msTransition': 'MSTransitionEnd',
10			'transition': 'transitionend'
11		},
12		transEndEventName = transEndEventNames[ Modernizr.prefixed( 'transition' ) ],
13		support = { transitions : Modernizr.csstransitions };
14	function toggleOverlay() {
15		if( classie.has( overlay, 'open' ) ) {
16			classie.remove( overlay, 'open' );
17			classie.add( overlay, 'close' );
18			var onEndTransitionFn = function( ev ) {
19				if( support.transitions ) {
20					if( ev.propertyName !== 'visibility' ) return;
21					this.removeEventListener( transEndEventName, onEndTransitionFn );
22				}
23				classie.remove( overlay, 'close' );
24			};
25			if( support.transitions ) {
26				overlay.addEventListener( transEndEventName, onEndTransitionFn );
27			}
28			else {
29				onEndTransitionFn();
30			}
31		}
32		else if( !classie.has( overlay, 'close' ) ) {
33			classie.add( overlay, 'open' );
34		}
35	}
36	triggerBttn.addEventListener( 'click', toggleOverlay );
37	closeBttn.addEventListener( 'click', toggleOverlay );
38})();