You need to add width and height rules in the sprite class to match the size of the icon in the sprite that you need.
Also try adding the icon as a pseudo element - like so:
.sprite:before {
content:'';
display: inline-block;
background:url("http://lorempixel.com/400/200/food") -50px -50px no-repeat transparent;
margin-right:5px;
color:red;
width: 20px;
/* icon width */
height: 20px;
/* icon height */
vertical-align: middle;
}