/*	Retina media query.
	Overrides styles for devices with a 
	device-pixel-ratio of 2+, such as iPhone 4.
-----------------------------------------------    */

@media 
	only screen and (-webkit-min-device-pixel-ratio: 2),
	only screen and (min-device-pixel-ratio: 2) {
	
	body {
	
	}
	
}

http://lessframework.com/

I took it from lessframework.

Target retina screen with mediaquery

css

CSS