How did this guy do this Hover?

Site URL: https://www.shortstache.com/personal

Notice the images size of the simple grid matches the background size. Done with a portfolio and a simple grid I believe but I can't get my image to be the same size. 

I'm not seeing any hover effects. I do see a lightbox effect.

Can you post a screenshot of where the hover effect is and the URL if different from above?

I figured it out. 

<style>
  div#gridThumbs {
padding: 0;
display: block !important;
}
.grid-image {
padding-bottom: 25% !important;
border-bottom: 5px solid #fff;
}
</style>