This page features Progressive Enhancement (breaking at 600px for tablet and 1141px for desktop) and as well as a reset by Eric Myers and a natural Box Model reccomented by Paul Irish

 

The phone CSS is the default. This should be RED for all devices

The tablet CSS adds to the phone CSS. On a tablet and above, this should be GREEN

The Desktop adds to the tablet which adds to the phone. On a desktop this should be BLUE