Examine source code of Nice Grey Gradient

{
  "theme": {
    "images": {
      "theme_frame": "firefox.jpg"
    },
    "colors": {
      "frame": "#787878",
      "tab_background_text": "#242424"
    }
  },
  "version": "2.0",
  "name": "Nice Grey Gradient",
  "manifest_version": 2,
  "description": "Grey gradient that should fit 1280x800 perfectly."
}