I'm using Commerce Kickstart (Version 2).
I created a new theme, which is basically a copy of the commerce_kickstart_theme. So it's a subtheme of omega_kickstart which is, itself, a subtheme of omega v3.
Even though the child theme has various css files for global, narrow, normal, it -looks- as though the theme actually reads in the css from the parent theme... ie. the OMEGA and is ignoring same-named files in my subtheme.
Eg. if I have a file global.css in my subtheme, it is ignored and the omega_kickstart/global.css is used instead.
The same goes for the various alpha files. Eg. I copied alpha-mobile.css into my theme folder. But the file being @imported is the /omega/alpha/css/alpha-mobile.css.
My understanding is that if a same-named css file was in your theme directory it -replaced- the file from the parent. But that doesn't seem to be happening.