How to change color for the rest of the window in browser?

Basically the title says it all, but the long story is bellow.

I need to have the rest of the screen black, when the game is running in the window. If you run the game in browser, there is your specified window where your gaming awesomness happens. And I need to change the color of the rest of the browser window.

Defaultly set to black, but when I fiddled with my project I accidentally somehow changed it to white (maybe because I tried Splaash plugin that set the color to something else).

I tried to change the collor of background, but no luck there. So how can I change the color? That is the ultimate question

Still no answer? I would really use the solution, because on mobile devices it makes a nasty two white lines on side of the screen (if the resolution is slightly different than the intended one). If those lines would be at least black, it wont be that annoying

There has to be a way how to change color of the window!

Sorry, I don't understand the question.

You're saying you previously managed to change the colour of the browser itself?

Well, I don't think it is the browser itself. But the background of the window in browser. It is black by default, so I somehow managed to change it. And I don't know how.

Looks like the layout colour. Have a look at the background colour in the layout editor. Bottom layer. Should show a white box. Change it to black.