<!DOCTYPE html>
<html>
<style>
.box {
width: 300px;
height: 300px;
}
.rgb-background {
background-color: green;
@media (-webkit-min-device-pixel-ratio: 2) {
width: 150px;
height: 150px;
</style>
<body>
<div class="box rgb-background"></div>
</body>
</html>