Setting transparency
I have this image that was originally created as an EPS file with whatever version of Illustrator was current in the mid-90s. I'm now using the latest version of Illustrator CC. The transparency grid shows that everything outside of the toys is transparent. I can select the two paths that make up the rectangle border and fill in with a color. I want the white area inside the rectangle to be transparent like the outside, but when I go into the transparency options and set the opacity to 0, it fills with the color of the rectangle that I just set! How do I get this area to go to true transparency? The icon just above the transparency group is greyed out so maybe there's a compatibility issue? Do opacity masks and/or knockout groups come into play? This is probably really easy but I'm a total Illustrator noob! Thanks.

