Examine source code of Cool Grey + White

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "Cool Grey + White",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/bg-017-7074520d97b5c592d413aed5f115f093.svg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(179, 179, 179)",
      "toolbar_text": "rgb(127, 127, 127)",
      "frame": "rgb(182, 182, 182)",
      "tab_background_text": "rgb(100, 100, 100)",
      "toolbar_field": "rgb(178, 178, 178)",
      "toolbar_field_text": "rgb(114, 114, 114)",
      "tab_line": "rgb(83, 83, 83)",
      "popup": "rgb(255, 255, 255)",
      "popup_text": "rgb(130, 130, 130)",
      "tab_loading": "rgb(83, 83, 83)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{297bbd70-99ac-4d03-8349-aa620806e8fd}"
    }
  }
}