You could try something like this. Add the class 'dashboard-icon-container' to the container, and then add the following CSS to your stylesheet. The glyphicon used by Mendix is already a font, so you can increase its size by using font-size.
.dashboard-icon-container {
position: relative;
}
.dashboard-icon-container .mx-link .glyphicon {
position: absolute;
width: 100%;
text-align: center;
font-size: 10em;
}
Get a character from font awesome and play around with opacity and z-order