You can leverage the CodeMirror plugin in order to make it easier to users to write HTML and CSS code into the CKeditor form element. You can download it here:
http://ckeditor.com/addon/codemirror
From there you can create a new directory:
mkdir app/assets/javascripts/ckeditor/plugins/And copy the full codemirror directory into the new plugins folder. From there you can copy the code from the addon page into the ckeditor/config.js file.