There you go.
But either way, Flightcrew probably shouldn't be giving it the old "
This resource is present in the OPF <manifest>, but it's not reachable (it's unused)" yada-yada. If having manifested resources that are only referenced via CSS (not in any xhtml) is valid under any circumstances
at all, it (Flightcrew) should probably understand that such resources
are, in fact, being used.