Swapping css for browser resolution- reference screen width?

Hello.

I’m currently saddened I cant reference the browser width in ruby. I’m
trying to use a periodically_call_remote function to trigger a ruby
function to change my css based on screen resolutions, but i cant pull
the screen resolution into a ruby variable!!

How can you do this? I tried a conditional in my
periodically_call_remote, so i can trigger a function call for one
resolution, but not other!

(this is for swapping iphone resolutions)

anyone?