Customizing The Login Page

Is it possible to customize the login page at:
https://www.nytix.com/amember/member

Change title, color, add artwork etc.
If so, which page should I be editing?

Obviously not on Configuration/Forms/Editor

this must be the dumbest question ever - which would explain the lack of response

You can completely customise the page by using your own theme and change the colours used etc. by including the new css files in file called 'site.css'.