Examine source code of Gray Tranquillity

{
  "description": "Theme with a single image placed centrally and then tiled. See https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Examples#themes",
  "manifest_version": 2,
  "name": "Gray Tranquillity",
  "version": "3.0",
  "homepage_url": "https://github.com/shellkr/",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "tranq_bg2.png"
      ],
      "theme_frame": "empty.png"
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "#353539",
      "tab_text": [
        250,
        99,
        23
      ],
      "frame": "#2a2a29",
      "tab_background_text": "#fff"
    }
  }
}