Examine source code of Green notification icon

{
  "manifest_version": 2,
  "name": "Green notification icon",
  "version": "1.0",
  "description": "The green notification icon is usually a green check mark next to a username or page, meaning it is verified.",
  "icons": {
    "48": "icon.png"
  },
  "browser_action": {
    "default_icon": "icon.png",
    "default_popup": "popup.html",
    "default_title": "Click me!"
  },
  "permissions": [
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{82e72f49-c059-4e6e-828d-e7c9d53928ef}"
    }
  }
}