Examine source code of Simple Sky

{
  "name": "Sky",
  "manifest_version": 2,
  "version": "1.0",
  "theme": {
    "images": {
      "theme_frame": "52492177595_30c17f967f_o(2).jpg"
    },
    "colors": {
      "frame": "rgba(229, 230, 232, 1)",
      "tab_background_text": "rgba(0, 0, 0, 1)",
      "toolbar": "rgba(79, 122, 181, 1)",
      "tab_line": "rgba(255, 255, 255, 1)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{5aacda8d-bf35-4b71-a332-e9e11d010933}"
    }
  }
}