CSS suggestion refering to http://www.cloudfour.com/examples/mediaqueries/image-test/

gistfile1.html

<style type="text/css">
@media all and (min-width: 501px) {
    #test5 {background-image:url('test5-desktop.png');width:200px;height:75px;}
}
@media all and (max-width: 500px) {
    #test5 {background-image:url('test5-mobile.png');width:200px;height:75px;}
}
/* ------------------------
Safari/WebKit parser barrier
Safari and WebKit mobile won't parse beyond this point
------------------------ */
@charset "utf-8";
#test5 {background-image:url('test5-desktop.png');width:200px;height:75px;}
</style>