So Negative Padding Is A Thing...

But you have to do some special stuff to get it.

First, use one of these bad boys

Then you have to be creative with your padding rules, because they don't like to be told outright to use a negative padding. Fortunately, both of these gentlemen are pretty dumb and can be easily confused with math.

.parent {
  border: 2px solid black;
  padding: 20px calc(20px * -1);
}
.child {
  border: 2px solid red;
}

And this is the result

I styled this so you would see how the code sample above would render in IE/Edge since I hope you aren't using that to look at this pen right now. You'll just have to trust me that this is what would happen. Or duplicate it and test it on your own.