Examine source code of Dark!

{
  "name": "Dark!",
  "manifest_version": 2,
  "version": "2.0",
  "theme": {
    "images": {
      "theme_frame": "blank.png"
    },
    "colors": {
      "frame": "rgba(41, 51, 69, 1)",
      "tab_background_text": "rgba(233, 172, 184, 1)",
      "toolbar": "rgba(41, 51, 69, 1)",
      "bookmark_text": "rgba(233, 172, 184, 1)",
      "toolbar_field": "rgba(61, 71, 99, 1)",
      "toolbar_field_text": "rgba(233, 172, 184, 1)",
      "tab_line": "rgba(233, 172, 184, 0.3)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{013c3c88-e98c-4004-a6f3-93ee3c04a779}"
    }
  }
}