Black masking tape. It's not opaque enough to block the light entirely; this means you can do a few layers to dim it to taste. Once that's sorted, a quick trim

Black masking tape. It's not opaque enough to block the light entirely; this means you can do a few layers to dim it to taste. Once that's sorted, a quick trim with an x-acto blade will tidy up the edges and make it all look intentional from a distance.