CRT television border from libretro's common-overlays (borders/tv-integer.cfg + borders/img/tv-integer.png), licensed CC-BY-4.0: https://github.com/libretro/common-overlays

overlay.cfg is the upstream file, unmodified. It is the reference DESKTOP skin: 1920x1080, descs = 0 (pure decoration, no touch buttons), and a viewport naming the transparent screen hole, so the Game Boy picture is fitted into the TV's tube instead of the whole window.