In pure CSS, no you cannot do math. It is strictly a styling language. There are a few options when it comes to dynamically styling your page.
You can use SASS and LESS, which are their own languages, run through a processor (SASS uses Ruby, LESS uses JavaScript) to generate the stylesheet.
The second option would be to use JavaScript, and for a beginner, jQuery would probably be the easiest option. Once you have included the jQuery source using something like <script src="js/jquery.js"></script>
(or alternatively the Google CDN), you are free to utilize the jQuery library in addition to standard JavaScript.
A short snippet to get the height of an image:
<script>
var imgHeight = $('.icon').height(); //remove the height and width from your CSS first!
var imgWidth = $('.icon').width();
</script>
You can then use jQuery to manipulate the CSS dynamically based on the height of the background image:
<script>
var iconA = $('.AAIcon');
iconA.css('background-position','imgHeight');
</script>