Modal image/lightbox not working; full image loads in new page

We are using the infinity scroll at http://coastmetalsolutions.com/new/gallery.html

Please check the top-left thumb titled "Test Title," with the + icon.

When you click the plus icon, instead of loading the full-size image as a modal dialog per lightbox, the full image loads in a new page.

The code seems alright:

<article class="portfolio-item pf-fiber-trims pf-before-after">
	<div class="portfolio-image">
		<img src="images/portfolio/4/1.jpg" alt="Sample Pic">
		<div class="portfolio-overlay">
			<div class="portfolio-desc">
				<h3>Test Title</h3>
			</div>
			<a href="images/portfolio/full/1.jpg" class="left-icon" data-lightbox="image"><i class="icon-line-plus"></i></a>
		</div>
	</div>
</article>

Let me know if you have an idea why this modal image isn't working.

Thanks in advance,
Paul

It's because I forgot to link magnific-popup.css at the top. :)