Examine source code of System Dark

{
  "manifest_version": 2,
  "version": "1.1",
  "name": "System Dark",
  "theme": {
    "images": {},
    "properties": {},
    "colors": {
      "toolbar": "rgb(60, 60, 60)",
      "toolbar_text": "rgb(255, 255, 255)",
      "frame": "rgb(34, 34, 34)",
      "tab_background_text": "rgb(255, 255, 255)",
      "toolbar_field": "rgb(34, 34, 34)",
      "toolbar_field_text": "rgb(255, 255, 255)",
      "tab_line": "rgba(255, 255, 255, 0)",
      "popup": "rgb(34, 34, 34)",
      "popup_text": "rgb(255, 255, 255)",
      "ntp_background": "rgb(34, 34, 34)",
      "tab_loading": "rgba(255, 255, 255, 0)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{36e74a87-518b-4865-acba-eeb260986dbb}"
    }
  }
}