Examine source code of maybe dark theme

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "dark",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/bg-000-5672c42860d5b06e1058dc477397f3ef.svg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(19, 44, 51)",
      "toolbar_text": "rgb(242, 202, 201)",
      "frame": "rgb(28, 28, 28)",
      "tab_background_text": "rgb(242, 202, 201)",
      "toolbar_field": "rgb(28, 28, 28)",
      "toolbar_field_text": "rgb(242, 202, 201)",
      "tab_line": "rgb(27, 40, 45)",
      "popup": "rgb(19, 44, 51)",
      "popup_text": "rgb(242, 202, 201)",
      "button_background_active": "rgba(0, 0, 0, 0)",
      "ntp_background": "rgb(34, 32, 46)",
      "ntp_text": "rgb(254, 223, 225)",
      "popup_border": "rgba(125, 185, 222, 0)",
      "popup_highlight": "rgba(125, 185, 222, 0.43)",
      "tab_loading": "rgb(204, 84, 58)",
      "tab_text": "rgb(254, 223, 225)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{4464e347-e76b-4c91-9d42-0748a3813703}"
    }
  }
}