YUI().use('node', 'overlay', 'widget-anim',  'event', function(Y) {
    var content = Y.one('#content'),
        overlay = new Y.Overlay({
        zIndex: 100,
        srcNode: '#loadingOverlay',
        width: content.getComputedStyle('width'),
        height: content.getComputedStyle('height'),
        centered: true,
        constrain: content,
        render: true,
        visible: false,
        plugins:[{
            fn:Y.Plugin.WidgetAnim, 
            cfg: {
            duration: 0.35
        }}]
    });
    Y.one('a').on('click', function(e){
            overlay.show(true);
            var timer=Y.later( 1500, this, function(){
                content.setContent(Y.one('#newContent'));
                overlay.hide(true);
            }  , null,  false);
        e.preventDefault();
        e.target.setStyle('visibility','hidden');
        
    });
});

<div id="loadingOverlay">
    <p>&nbsp;</p>
</div>
<a href="#">Test</a>
<div id="content">
<ul>
<li>Lorem ipsum dolor sit amet, consectetur adipiscing elit.</li>
<li>Maecenas rutrum lacus tellus, et porta ante.</li>
<li>Vestibulum vel lorem quis lectus facilisis volutpat at ut sapien.</li>
<li>Maecenas vitae eros porta velit pulvinar condimentum at non nisi.</li>
<li>Sed vehicula libero augue, in ultrices dui.</li>
</ul>
 <ul>
<li>Aenean elementum nunc at nulla euismod molestie.</li>
<li>Sed commodo est at ante rhoncus sollicitudin.</li>
</ul>
 
</div>
<div id="holder">
    <div id="newContent">
<ul>
<li>Duis in augue felis, quis gravida dolor.</li>
<li>Aenean facilisis ante leo, et dignissim orci.</li>
</ul>
<ul>
<li>Fusce eu felis sed mi faucibus cursus.</li>
<li>Proin fermentum hendrerit nunc, ac facilisis purus pretium quis.</li>
</ul>
<ul>
<li>Sed nec risus eget sem gravida accumsan.</li>
<li>Nunc vel mauris vitae nunc porttitor pellentesque.</li>
 
</ul>
    </div>  
</div>

body {
  padding: 50px;
  font: 14px "Lucida Grande", Helvetica, Arial, sans-serif;
}

a {
  color: #00B7FF;
    margin-bottom:20px;
    display:block;
}
.yui3-overlay-mask { 
    background: rgba(255, 255, 255, 0.75);  
}

.yui3-widget #loadingOverlay {
    display: block;
    background: rgba(0, 0, 0, 0.5);
    background-position: center center;
    background-image: url('http://samples.apphb.com/ajax-loader-bar.gif');
    background-repeat:no-repeat;
    padding: 10px;
    color:#ffffff;
    margin:1px;
}

ul{padding:4px;}

#holder {display:none;}

jsFiddle