You can easily set up a custom css for TinyMCE to use to get a more similar look n feel. If you just need a generic site wide css styling you can use web.config settings
<episerver> <applicationSettings ... uiEditorCssPaths="~/Static/css/Editor.css" /> </episerver>
See documentation here for how to point out css file to use and how to override some styles etc
As per the title...
(I've seen a couple of posts that are roughly on this topic.... but answers were vague in both cases.)