Strange... If you have Firefox, install Firebug and you may check the styles, and discover which parts of the code that is not working. See attached example: firebug.png

Rgds

FIXED

the problem is :
default path
a.facebook {background-image: url(../images/social/facebook.png);}

the images folders in K2 customized templates are in the second level so...
a.facebook {background-image: url(../../images/social/facebook.png);}

Great!

Rgds