Members of the EU have a class="eu", countries in europe (which I found turkey to be but russia not) have a class="europe".
Certain countries are further subdivided the United Kingdom has gb-gbn for Great Britain and gb-nir for Northern Ireland. Russia is divided into ru-kgd for the Kaliningrad Oblast and ru-main for the Main body of Russia. There is the additional grouping #xb for the "British Islands" (the UK with its Crown Dependencies - Jersey, Guernsey and the Isle of Man)

Contributors.
Original Image: (http://commons.wikimedia.org/wiki/Image:Europe_countries.svg) Jlio Reis (http://commons.wikimedia.org/wiki/User:Tintazul).
Recolouring and tagging with country codes: Marian "maix" Sigler (http://commons.wikimedia.org/wiki/User:Maix)
Improved geographical features: http://commons.wikimedia.org/wiki/User:W!B:
Updated to reflect dissolution of Serbia & Montenegro: http://commons.wikimedia.org/wiki/User:Zirland
Updated to include British Crown Dependencies as seperate entities and regroup them as "British Islands", with some simplifications to the XML and CSS: James Hardy (http://commons.wikimedia.org/wiki/User:MrWeeble)