Same z-index acting differently in different sites

I am seeing an error which I think is because of z-index, the error is really strange. See these two posts in two different sites (while keeping in mind that the data is same only the sites are having different css)

1st site (buggy one) :

2nd site (the okay one) :

To see the error please go to first site then click on PLAY and while keeping it open, kindly go to the 2nd on and then click on PLAY you will see the error that I am talking about, I am not able to understand what’s going on?

I see the difference between the two, but what exactly is the issue? I’m not seeing anything terribly wrong, to the point I’d need it fixed (I do see discrepancies, although I’d prefer just to fix the ACTUAL issue)

what do you mean its not a issue, the content is appear inside the game, like if it has created holes into it, doesn’t it look likes an issue to you?

There is no content on the page to begin with?!

I take back my original statement. I DON’T see what the issue is. If I had seen what you described, I’d obviously think that’s an issue…

Take a screenshot. Post it please.