http://stephen.io/mediaqueries
@media (-webkit-min-device-pixel-ratio: 2), (min-resolution: 2dppx) {
}
@media only screen and (min-device-width : 320px) and (max-device-width : 568px) and (max-device-height: 568px) and (orientation : portrait) { /* iphone 5, 5s*/ }
@media only screen and (min-device-width : 320px) and (max-device-width : 480px) and (max-device-height: 480px) and (orientation : portrait) { /* iphone 4, 4s, 3, 2, 1 */ }