/* Input example */
.foo {
    background-image: image-set(url(img/test.png) 1x,
                                url(img/test-2x.png) 2x,
                                url(my-img-print.png) 600dpi);
}

/* Output example */
.foo {
    background-image: url(img/test.png);
}

@media (-webkit-min-device-pixel-ratio: 2), (min-resolution: 192dpi) {
    .foo {
        background-image: url(img/test-2x.png);
    }
}


@media (-webkit-min-device-pixel-ratio: 6.25), (min-resolution: 600dpi) {
    .foo {
        background-image: url(my-img-print.png);
    }
}