div上的CSS边框突然停止在chrome中工作。仍然适用于Firefox

So as the title already says, something weird happened just now. I was working on my memory game, after re-opening the page the border around the divs when navigating with keyboard arrows stopped showing up. (click in the window to get arrows to work.) I always use google chrome but now that this happened I went over to firefox and the border shows up there :sSo as the title already says, something weird h