Kiran - it's simpler than that if I'm understanding what you want to do - if you want to put in any custom css in the html editor - why not go to Admin/Settings/ scroll down the page and you'll see you can edit a CSS file which, is actually the portal.css file sitting in the portal ID folder - eg.. if your site is the primary on, eg. Portals/0/ in there you'll find a portal.css file and that's in every single portal that's deployed.

This gives you the ability to add extra classes without touching the skin file. I actually tell my clients to do this if they want to make some special changes.

Why don't you try and add the class via the Admin/Settings/Advanced - edit  css file .. click save file and then update.. then, it should appear in the dropdown selector - and you can add in html mode using div tags if you wish.

Does this help?

Nina Meiers