Examine source code of Dark Mode Toggle

{
  "manifest_version": 2,
  "name": "Dark Mode Toggle",
  "description": "Toggle dark mode for any website.",
  "version": "1.0",
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_title": "Toggle Dark Mode",
    "default_icon": {
      "16": "icons/icon.png"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "applications": {
    "gecko": {
      "id": "dark-mode-toggle@addon.local"
    }
  },
  "icons": {
    "48": "icons/icon.png"
  }
}