Random bug maybe, idk anything about making games, but sometimes the sky and ground have little lines? only in full screen, but really noticeable in the sand zone and in the sky. They also shift/move and flash I guess??
That happens because of how some browsers render the game's cells when the screen is scaled. It's called subpixel rendering, and it happens when the cells end up with tiny decimal values for their width or height, which can lead to those tiny gaps you noticed. This tends to happen on browsers like Chrome. If possible, I recommend playing on Firefox, since it doesn't have this issue. Hope that helps :)