Trouble adding image icons to footer nav menu

I added image icons to my Responsive Theme main nav menu by indenting the text out of view, placing a background image, and using sprite like so:

#menu-item-104 a {width:47px; background-position: -125px 0;}

This technique is not working for me in the footer menu. I can’t even move the menu text out of view. Am I missing something?

What can I do?