Examine source code of Toggle Dark Mode

{
  "manifest_version": 2,
  "name": "Toggle Dark Mode",
  "version": "1.0",
  "description": "Toggle dark mode for any website with one click.",
  "icons": {
    "48": "icon-48.png",
    "96": "icon-96.png"
  },
  "permissions": [
    "tabs",
    "activeTab"
  ],
  "background": {
    "page": "background.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "toggle-dark-mode@example.com"
    }
  },
  "browser_action": {
    "default_icon": "icon-48.png",
    "default_title": "Toggle Dark Mode"
  }
}