How do I get rid of this floating box on my Mac screen?

After installing High Sierra with the latest update, I now have a "floating box" that is centered around my mouse and follows whatever direction the pointer goes in. It doesn't obstruct my view; it is an open box that takes up 75% of the screen, but it is annoying just by being there. I have logged off and logged back on. I have restarted my computer. I have closed all apps. I tried to include a screenshot but the file is too big. I am not the most computer savvy person so any help that is easily understood and followed is greatly appreciated.