Examine source code of Countdown timer by Michal

{
  "manifest_version": 2,
  "name": "Countdown timer by Michal",
  "description": "Create, manage, and be notified for important events.",
  "version": "2.0.0",
  "icons": {
    "128": "icon/128.png"
  },
  "permissions": [
    "storage",
    "notifications",
    "alarms",
    "tabs"
  ],
  "author": "Michał Futera",
  "homepage_url": "https://michalfutera.pro",
  "browser_specific_settings": {
    "gecko": {
      "id": "countdown-timer@michalfutera.pro",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "chrome_url_overrides": {
    "newtab": "newtab.html"
  }
}