Examine source code of This extension lets

{
  "manifest_version": 2,
  "name": "Dark Mode Toggle",
  "version": "1.0",
  "description": "Toggle dark mode on the current website with one click.",
  "browser_action": {
    "default_popup": "popup/popup.html",
    "default_icon": {
      "48": "icon.png"
    }
  },
  "permissions": [
    "activeTab"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{76dc942a-39fd-4082-93a9-031f49c2f3cd}"
    }
  }
}