Examine source code of Terraria Forest

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "Terraria Forest",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/0.png"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "center center"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(3, 109, 59)",
      "toolbar_text": "rgb(81, 47, 2)",
      "frame": "rgb(7, 7, 7)",
      "tab_background_text": "rgb(194, 246, 198)",
      "toolbar_field": "rgb(1, 144, 77)",
      "toolbar_field_text": "rgb(115, 66, 1)",
      "tab_line": "rgb(81, 47, 2)",
      "popup": "rgb(1, 144, 77)",
      "popup_text": "rgb(65, 38, 2)",
      "tab_loading": "rgb(81, 47, 2)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{06ff388f-5bc4-4114-8362-bde7c63f8ca9}"
    }
  }
}