Examine source code of Celebrate....

{
  "theme": {
    "images": {
      "theme_frame": "CelebrateHCustom.jpg"
    },
    "colors": {
      "frame": "#000000",
      "tab_background_text": "#ffffff"
    }
  },
  "version": "2.0",
  "name": "Celebrate....",
  "manifest_version": 2,
  "description": "4th of July, America, big city, bright, buildings, city, collage, fireworks, flags, Independence Day, lights, New Years, New York, night, proud, reflection, speakers, Stature of Liberty, tree, United States, USA, water\t\n\nDesigned by MaDonna\n\nMy wallpaper to match is at: <a href=\"https://outgoing.prod.mozaws.net/v1/88aee036d8d54019f9def44e554f8212e864e64ffedadcd0c3220a9d5fbca98f/http%3A//abstract.desktopnexus.com/wallpaper/1084343/\" rel=\"nofollow\">http://abstract.desktopnexus.com/wallpaper/1084343/</a>"
}