Examine source code of Transparent Rainbow

{
  "manifest_version": 2,
  "version": "4.1",
  "name": "Transparent Rainbow",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/0.png"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "center center"
      ],
      "additional_backgrounds_tiling": [
        "no-repeat"
      ]
    },
    "colors": {
      "toolbar": "rgba(0, 0, 0, 0.39)",
      "toolbar_text": "rgb(255, 255, 255)",
      "frame": "rgb(140, 140, 140)",
      "tab_background_text": "rgb(0, 0, 0)",
      "toolbar_field": "rgba(0, 0, 0, 0.44)",
      "toolbar_field_text": "rgb(255, 255, 255)",
      "tab_line": "rgba(0, 0, 0, 0)",
      "popup": "rgba(0, 0, 0, 0.44)",
      "popup_text": "rgb(255, 255, 255)",
      "tab_loading": "rgba(0, 0, 0, 0)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{81f6c5fb-4425-4209-8255-90def7d59215}"
    }
  }
}