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