It is just CSS which controls this section. Here it is,

.projects-grid .fancybox-thumb span:before {
background: #5cb85c url(images/icons.png) no-repeat scroll 11px -108px;
content: "";
display: block;
height: 40px;
left: 50%;
margin-left: -20px;
margin-top: -20px;
position: absolute;
top: 50%;
width: 40px;

It’s located on line 708 of the style.css file.

If you have any other questions please let me know.