Examine source code of Metroid Dark Theme

{
  "manifest_version": 2,
  "version": "1.1",
  "name": "metrid",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/0.jpg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "left center"
      ],
      "additional_backgrounds_tiling": [
        "no-repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(0, 0, 0)",
      "toolbar_text": "rgb(11, 185, 238)",
      "frame": "rgb(0, 0, 0)",
      "tab_background_text": "rgb(140, 140, 140)",
      "toolbar_field": "rgb(0, 0, 0)",
      "toolbar_field_text": "rgb(255, 255, 255)",
      "tab_line": "rgb(11, 185, 238)",
      "popup": "rgb(0, 0, 0)",
      "popup_text": "rgb(255, 255, 255)",
      "tab_loading": "rgb(11, 185, 238)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{18f292f9-6ad7-4a05-b330-d1a19190f7f4}"
    }
  }
}