Examine source code of Gradient sky

{
  "theme": {
    "images": {
      "theme_frame": "Firefoxheadergradientsky.jpg"
    },
    "colors": {
      "frame": "rgba(229,230,232,1)",
      "tab_background_text": "#e8ebf0"
    }
  },
  "version": "2.0",
  "name": "Gradient sky",
  "manifest_version": 2
}