If you want to override application styles etc. Edit this file if you want to override standard CSS styling
Edit this file if you want to override widget styles
I also suggest to have a look at http://livehelperchat.com/how-to-make-unbranded-version-of-live-helper-chat-223a.html this article. There is prepared extension for all things you may need to customise the app.
Developing application takes a lot of time. You can support application by donating. There is no company behind this application and it takes away my free time. Every donation matters and does not matter how small it is!