turning a div into transparent to see through two containers

Question

I have following markup

Answer 1

The 4th number in rgba() is the alpha transparency. You've set it to 0, which is completely transparent. 1 would be completely opaque. You need to set that to some value between 0 and 1.

That said, if you are trying to create the effect of a hole, then what you need to do is create a background image that is white and has a transparent circle cut in it and make that the background to .holder. It doesn't matter how transparent you make .circle if .holder is completely opaque!