Please add a close button to the top right corner of the box. If I view on a mobile device, there's no way to close the pop-up, and keep reading. If I click on another reference to try to close the box, I'm taken to your site. I don't mind going to your site occasionally, and I want my readers to have that option. But they shouldn't suddenly be taken there without warning or intention. A simple button to close the pop-up would be very helpful.