gpEasy 2.0 introduces true inline WYSIWYG editing, therefore, the follow is now deprecated. Please see the True WYSIWYG page for documentation on how to ensure that your theme works properly with True WYSIWYG editing.
If you want your user to have a more immervise editing experience you can inherit your CSS to the CKeditor <iframe>. To do so, edit the file /include/css/ckeditor_contents.css as follow:
Note that this is a recent hack that I don't test a lot, but the possible break out should be limited as we are working in a <iframe> context.
You also should be aware that if you select another theme for your installation, you will have to update the path to the theme used in CKeditor.
When using this hack if you copy and paste within CKEditor the pasted text will be formatted as per your theme's css. This means that there will be unnecessary, basically duplicate, code with every pasted section of formated text that you copy from within CKEditor and past within it in another area. The reasons is simple, the browser is formatting the text within CKEditor as per your theme's css, instead of raw formatting, thus any text copied will be copied with its formatting applied and therefore the formatting is added when pasted to another section within CKEditor. This is no different than copying text from another web page or document; however, additional code generation is generally not expected when copying & pasting within the same document/editor. . . nonetheless, with this hack it will occur with formatted text.