chromium/third_party/blink/web_tests/fast/media/mq-min-pixel-ratio.html

<html>
<head>
<title>CSS3 media query test: Device-pixel ratio query. Using style element, @media css rule.</title>
<style type="text/css">
@media  screen and (-webkit-min-device-pixel-ratio: 1) {
    div {
        background-image: url(resources/apple_logo_half_size.png);
    }
}

@media  screen and (-webkit-min-device-pixel-ratio: 2) {
    div { 
        background-image: url(resources/apple_logo_big.jpg); 
        -webkit-background-size: 320px 240px;
    }
}
</style>
</head>

<body>
<div style="width:320px; height:240px;"></div>
</body>
</html>