A (control): one url(). Expected and actual: photo.
B (control): gradient first, then url(). Expected and actual: darkened photo.
C: url() first, then gradient. Expected: small centred photo on a red-to-blue gradient. Actual: small photo on grey, the gradient is gone.
D: two url() layers. Expected: small centred tile on a full-size photo. Actual: only the small tile on grey, the photo is gone.