What does -webkit-min-device-pixel-ratio: 2 stand

Question

@media only screen and (max-device-width:480px), 
only screen and (-webkit-min-device-pixel-ratio: 2)
{ /*iphone css*/ }

max-device width makes sense but pixel ratio doesn't make any sense to me. thanks.

Answer 1

From http://developer.android.com/reference/android/webkit/WebView.html

The -webkit-device-pixel-ratio CSS media query. Use this to specify the screen densities for which this style sheet is to be used. The corresponding value should be either "0.75", "1", or "1.5", to indicate that the styles are for devices with low density, medium density, or high density screens, respectively. For example: The hdpi.css stylesheet is only used for devices with a screen pixel ration of 1.5, which is the high density pixel ratio.

And according to https://developer.mozilla.org/en/CSS/Media_queries

-moz-device-pixel-ratio

Gives the number of device pixels per CSS pixel.

Note: This media feature is also implemented by Webkit as -webkit-device-pixel-ratio. The min and max prefixes as implemented by Gecko are named min--moz-device-pixel-ratio and max--moz-device-pixel-ratio; but the same prefixes as implemented by Webkit are named -webkit-min-device-pixel-ratio and -webkit-max-device-pixel-ratio.