Sorry Sebastian, of course you are right! :-)
This is the original Post from the FCKEditor website about this topic:

You can precisely simulate the output of your site inside FCKeditor, including background colors, font styles and sizes and custom CSS definitions. To do that, just point this setting to the CSS file that you want the editor to use. You may use a simple string, setting the CSS file path, or even a string array, with more than one CSS file to be loaded. Example:

FCKConfig.EditorAreaCSS = '/mycssstyles/editorstyle.css' ;

By default, FCKeditor uses a very simple file located at "editor/css/fck_editorarea.css". You can place your file outside the FCKeditor directory and just point to that.

I definitely mixed this up!

Thanks very much guys!

Problem solved. Much appreciated.