Examine source code of Fortress Wall

{
  "theme": {
    "images": {
      "theme_frame": "fortress_wall_header.jpg"
    },
    "colors": {
      "frame": "#ffffff",
      "tab_background_text": "#ffffff"
    }
  },
  "version": "2.0",
  "name": "Fortress Wall",
  "manifest_version": 2,
  "description": "Fortress Wall with arrow slits.  Based on royalty-free texture at <a rel=\"nofollow\" href=\"https://outgoing.prod.mozaws.net/v1/9f5a992c030f0b505e03c20a42c636bdfe7950c0b48e728b6817ada06aba29ca/http%3A//www.spiralgraphics.biz\">http://www.spiralgraphics.biz</a>"
}