In many Gavick templates such as coffee and black & white, the developers have been able to use PNG files containing a set of navigation icons. using the black and white example (http://demo.gavick.com/joomla15/oct2010/), the navigation arrows of READ THIS and HIT STORIES modules are all controlled by a single png containing a set of navigations icons each appearing depending on the state of the navigation( i.e. when you hover over a navigation arrow it will pick the second icon in the PNG file).
What i want to know is how is this achieved? i.e. what trickery is involved in combining png files and css to produce such navigation style
Sorry if i am not that clear, its the best i could describe what i want to ask
All answers are appreciated. cheers!