.class {
    background: none;
}

.class {
    background: image-set(url(foo.jpg) 2x);
}

.class {
    background-image: image-set(url(foo.jpg) 2x);
}

.class {
    background: filter(url('image.jpg'), blur(2px));
}

.class {
    background: filter(url('image.jpg'), blur(2px));
}

.class {
    background: url(image.jpg), filter(url('image.jpg'), blur(2px));
}