Styles referenced by the page that contains the editor does not apply to the editing region. Usually you can put all the styles that will be used by editor text into a separate .css file and then reference that file by setting the editor's TextAreaCssFile property.

When displaying the contents back to the user, you should make sure the page that is used to display the contents reference the same .css file the editor references so that the displayed contents have the same styles as they are in the editor.

If HtmlBodyCssClass is used on the editor to set the default text styles for the editor contents, the same CSS class usually should also be used while displaying the contents without the editor.