What resolution would be good to use for a game able to run on most popular resolutions?
And what size should my background image have not to show any empty space when scaling?
Any good advice?
Develop games in your browser. Powerful, performant & highly capable.
Supporting multiple screen sizes
There are so many different resolutions out there it does not make sense to target just one. It would be better to target a common aspect ratio and scale the game in letterbox mode.