Black square around close button in promotional pop-up

I've figured out how to customize my promotional pop-up a good deal, but I can't seem to get rid of this annoying black box around the close out button. See attached photo. Any ideas?

I also removed all of my custom code to see if anything funky was going on, but the box remained...

One quick follow up: the box only shows up on first load, and then if I click elsewhere on the page or in the pop-up it goes away.

The outline is there for assistive technologies. I suggest not removing it. It goes away when you take focus away from it.

Aha! Makes sense -- thanks for clarifying the function @creedon.