Examine source code of Dark Mode

{
  "manifest_version": 2,
  "name": "Dark Mode",
  "version": "1.0",
  "description": "Dark Mode for webpages",
  "browser_action": {
    "default_title": "Dark Mode",
    "default_popup": "popup.html"
  },
  "permissions": [
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "https://*.com/*",
        "https://*.org/*"
      ],
      "js": [
        "content_scripts.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{48e91a75-fe58-4179-9e40-aabbf2b8aea0}"
    }
  }
}