is this a BTT feature? How do I turn this off?

recently, I have this little box show up on my screen, and I haven't figured out how to turn it off. I am guessing that I accidentally toggled it with a keystroke, and I am guessing that it is BTT, but I can't figure it out. But I thought I'd ask if anyone recognizes it.

It looks like this, and it is the shortcut to switch tabs. It just floats above everything and blocks the view.