The functionality of CSS Class Dialog had exceeded the limits of an usual dialog's functionality. So it was moved to separate views. They are used for editing of CSS file and preview of CSS class.
http://content.screencast.com/users/transfer/folders/Default/media/41d05111-229d-44e1-9ec0-1f85052f4777/css_views.png
http://content.screencast.com/users/transfer/folders/Default/media/445a7ae8-ccb6-4e01-ae09-cd6659f4fd3b/css.swf
Here Jira link, related to this post https://jira.jboss.org/jira/browse/JBIDE-3445