Just a moment ago, something strange happened while I was working on my memory game. After reopening the page, the borders around the divs stopped showing up when navigating with the keyboard arrows. (Click in the window to activate the arrow keys.) Normally, I always use Google Chrome for this project, but out of curiosity, I tried opening it in Firefox and the borders were visible there. Strange, right?
Have you experienced the same thing?: http://jsfiddle.net/94jerdaw/USesV/
I highly doubt that it's an issue with the CSS since I haven't made any changes to it, at least not intentionally...
As mentioned earlier, make sure to click on the result frame to focus on it, and then check if the borders display correctly in chrome/Firefox:
$('#' + tar).addClass("target");
This line of code corresponds to this style:
.target{
width:94px;
height:94px;
border:3px solid black;
}