Examine source code of Outlook dark

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "Outlook dark",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/0.jpg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "center center"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(52, 52, 52)",
      "toolbar_text": "rgb(255, 255, 255)",
      "frame": "rgb(52, 52, 52)",
      "tab_background_text": "rgb(255, 255, 255)",
      "toolbar_field": "rgb(108, 108, 108)",
      "toolbar_field_text": "rgb(255, 255, 255)",
      "tab_line": "rgb(200, 200, 200)",
      "popup": "rgb(68, 64, 63)",
      "popup_text": "rgb(255, 255, 255)",
      "tab_loading": "rgb(200, 200, 200)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{d5d0fa04-880c-469c-87cb-d900834a0774}"
    }
  }
}