Examine source code of BetterDark

{
  "browser_specific_settings": {
    "gecko": {
      "id": "BetterDark@neopolitan.uk",
      "strict_min_version": "65.0"
    }
  },
  "manifest_version": 2,
  "version": "1.1",
  "name": "BetterDark",
  "theme": {
    "colors": {
      "frame": "#151515",
      "icons_attention": "#fff",
      "ntp_background": "#202020",
      "popup": "#202020",
      "popup_border": "#303030",
      "popup_highlight": "#202020",
      "popup_text": "#fff",
      "sidebar": "#202020",
      "sidebar_border": "#303030",
      "sidebar_text": "#fff",
      "tab_background_text": "#fff",
      "tab_line": "#303030",
      "toolbar": "#202020",
      "toolbar_bottom_separator": "#303030",
      "toolbar_field": "#151515",
      "toolbar_field_text": "#fff",
      "toolbar_top_separator": "#303030"
    }
  }
}