This is a Greasemonkey/Tampermonkey script that re-styles an SE site to look like stackoverflow.com
Download / Install:
You can install either the site or the chat version on Greasy Fork (works with Tampermonkey and Greasemonkey)
This is a JS script, so it's easy to modify if you want.
This script is very minimal and there is no promise it will work on every site. The more customized a site is, the less this will work (photo.se for example). If you have need of a specific site to be accounted for, let me know and I may be able to add some code to handle it.