Lovelace Background Opacity

Hi, I’m having trouble adding opacity to my lovleace View background image.
I can add the image just fine by adding the following to my view yaml editor:

background: >-
100% / cover no-repeat fixed url(‘/local/House/2nd Floor - Master

I am unsure how to add opacity though. It looks like hacs card-mod doesn’t inject the css in the right spot for this to work. Does anyone have any experience with this?

Did you ever figure this out? I have been trying to do the same for a while with no luck