Screen profile and screen resolution modification to CSS file

If I change the minimum screen resolution for a screen profile (I want to make the minimum desktop resolution 1000 px wide) I get a message saying I need to "ManageMedia Queries in the Styles dialog box and map undefined media queries". I believe I need to edit a CSS file to do this, but which one? If I change the minimum resolution for the desktop profile do I also need to change the maximm resolution for the Tablet profile?