Although I love sites that actually uses the same look for editing pages:
To compete with others (and to say: yes to job requirements like: 'do you have a preview functions'.
Is there a way to set up 'preview' of 'pages' before saving - if you only theme for frontend ?
Please use the plone.app.iterate AddOn. CheckIn/Checkout a Workingcopy of Content Type, edit the Copy and replace the Original if you happy with the Result. I think this is the "Preview" Way.
castle cms has this feature. http://castlecms.io. I think its one of many excellent ideas that should be brought into the plone core. I think it might even be possible to have a sidebyside auto updating preview.
Here is a place to discuss this idea further - https://github.com/plone/Products.CMFPlone/issues/907