You have a wrapping element that comes after your icon elements, and so you icons have been placed underneath in the z direction (into the page).
Now if you were to put the icon element within the wrap, this would probably automaticy fix the z-index's. If you don't want to do that or don't know how and just want a hack you can change the z-index of the icons containing element to something high (I did 5 and that worked). BUT if you read http://www.w3schools.com/cssref/pr_pos_z-index.asp you will see that "z-index only works on positioned elements (position:absolute, position:relative, or position:fixed)." and your icon element has no positioning, so you need to give it position: relative
Some extra reading on z-index's. http://css-tricks.com/almanac/properties/z/z-index/
Cheers,
-Adrian