Examine source code of 3-2-1

{
  "manifest_version": 2,
  "version": "2.0",
  "name": "Celebrate",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/0.jpg",
        "images/1.jpg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "left center",
        "center center"
      ],
      "additional_backgrounds_tiling": [
        "repeat",
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgba(225, 234, 239, 0)",
      "toolbar_field": "rgba(255, 255, 255, 0)",
      "toolbar_field_text": "rgb(243, 240, 169)",
      "tab_line": "rgb(248, 246, 112)",
      "popup": "rgb(237, 223, 154)",
      "popup_text": "rgb(156, 116, 34)",
      "tab_loading": "rgb(248, 246, 112)",
      "bookmark_text": "rgb(218, 215, 216)",
      "frame": "rgb(201, 189, 142)",
      "tab_background_text": "rgb(236, 223, 223)"
    }
  }
}