How can I load each file selectively depending on client in a package?

I am making my own Meteor package for Ratchet.
Ratchet has each theme css for iOS and Android.

Are there any descriptions in package.js that allow me to load a them css file depending on client devices?
I imagine the code below

if (isIOS(navigator.userAgent))
else if (isAndroid(navigator.userAgent))

but I know that it is impossible because Meteor collects all CSS files and compresses.

Any good ideas?