Examine source code of itdock

{
  "manifest_version": 2,
  "version": "1.2",
  "name": "Blue Star",
  "theme": {
    "images": {
      "theme_frame": "2.png",
      "additional_backgrounds": [
        "itdock.png"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "left"
      ]
    }
  }
}