Hi Kris,
you can use this in your dashboard specific css in order to include global aspects from "MYGLOBAL.css".
@import url('MYGLOBAL.css');
In my experience it is advisable to place both in one and the same folder. We created one "css-folder" including the global css and all dashboard specific css files.
See also:
Design Studio: Attach Multiple Custom CSS Files
Best Regards
Mark