Hello Gene,
I have been able to recreate the issue you describe when I am zoomed in on the web page at 250%, for the time being you will need to zoom out just a bit to reveal the X in the top righthand corner of the video player.
You can do this by holding the CTRL key on your keyboard and using your mouse’s scroll wheel to zoom in and out. I have put in a ticket with our dev to see if he can come up with a solution.