Masonry brick background color?

Hey, it´s me again :)

I was just wondering how to change the background color of the masonry bricks only?

I know they change with the background color of the content when adjusted in the customizer, but I would like to change the color of masonry bricks exclusively.

I tried to add this in my custom css

.masonry-brick {
  background-color: #f1f1f1 !important;
	
	
	}

But the background color did not change...

What CSS would I need to add to change the background color of the masonry bricks?

Kind regards

Are Martin