:root {
    --image-path-stylesheet: url("/prx/000/http/wpt.live/css/css-values/urls/support/images/test.png");
}

#stylesheet-relative-image {
    background-image: url(/prx/000/http/wpt.live/css/css-values/urls/support/images/test.png);
}

#stylesheet-relative-variable-image {
    background-image: var(--image-path-stylesheet);
}

#stylesheet-relative-document-variable-image {
    background-image: var(--image-path-document);
}