Examine source code of UnderscoreTheme v3.0.1

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "UnderscoreTheme v3.0.1",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/0.png"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "left top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(43, 43, 43)",
      "toolbar_text": "rgb(231, 231, 231)",
      "frame": "rgb(65, 65, 65)",
      "tab_background_text": "rgb(224, 224, 224)",
      "toolbar_field": "rgb(21, 21, 21)",
      "toolbar_field_text": "rgb(205, 205, 205)",
      "tab_line": "rgb(255, 178, 0)",
      "popup": "rgb(38, 38, 38)",
      "popup_text": "rgb(205, 205, 205)",
      "tab_loading": "rgb(255, 178, 0)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{60c2f4a9-2859-44a1-a77e-cfe7cabe6e56}"
    }
  }
}