Examine source code of Inject Scrpt & Style

{
  "manifest_version": 3,
  "name": "Inject Script & Style",
  "version": "1.0",
  "description": "Injects a small banner at the top of every page and a custom CSS rule.",
  "host_permissions": [
    "<all_urls>"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "inject.js"
      ],
      "run_at": "document_end"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "inject-script@example.com"
    }
  }
}