Examine source code of Nature At Night

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "Park at night",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/0.png"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "center center"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(7, 50, 84)",
      "toolbar_text": "rgb(67, 194, 218)",
      "frame": "rgb(14, 41, 65)",
      "tab_background_text": "rgb(24, 156, 180)",
      "toolbar_field": "rgb(38, 72, 102)",
      "toolbar_field_text": "rgb(67, 194, 218)",
      "tab_line": "rgb(67, 194, 218)",
      "popup": "rgb(7, 50, 84)",
      "popup_text": "rgb(24, 156, 180)",
      "tab_loading": "rgb(67, 194, 218)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{e4a83b18-53c9-4ab2-bcd7-562f3011476e}"
    }
  }
}