Problem in changing the fckeditor css

Actually i had used h1 to h6 as classes in user end, and when i had enter something from the backend i only view the text as simple <h1> tags but this text take class when viewed in user panel. In this client wants same format in both ends. So is there any way to change the css of fckeditor so that same reflection in user and admin panel.

If anybody knows please tell me asap (its very urgent).

Thanks & Regard
Vikas Pal