CSS and Its versions

References:
http://reference.sitepoint.com/css/css#css__fig_what-is-css_three-layers
http://reference.sitepoint.com/css/csshistory
http://www.w3.org/TR/CSS2/changes.html
http://webdesign.about.com/od/css2/a/aa090202a.htm
http://www.westciv.com/style_master/academy/css_tutorial/introduction/index.html#new
creating sexy style sheets - jina bolton