How to change the background of a mask?

Question

css

Hello, there is a problem. There is a 50x50 block, it should be red light, and the inner svg should be black, which is used as a mask. The mask is used so that when the block does not have the active class, the background becomes gray and the icon is white. I learned how to change the color of the icon, but I can't change the color of the block itself. Actually this is what it looks like now