Thanks for your help, newt
I tried it (by replacing #000 by #fff) and the only difference I saw was that the whole game was displaced maybe 20 pixels lower and a white bar has appeared on top of the image.
(image from Xcode's simulator, as you can see there's an undesired white bar on top of the image, but the borders are still black)
But that's not at all what I wanted to do. (having white bars of letterbox scale instead of black ones).
Maybe I put the code at the wrong place in the index.html file? I placed it below html, body {
I know nothing about HTML, so maybe I just didn't do what you intended?
Just as a side note, your first solution worked really well for Android,but sadly I only need it for iOS. :(
Further help would be greatly appreciated.