Examine source code of GCal Duplicate & Duration

{
  "manifest_version": 3,
  "name": "Google Calendar Duplicate & Duration",
  "version": "1.3",
  "description": "Adds a duplicate button to Google Calendar events and shows total duration of events in event cards.",
  "permissions": [
    "activeTab",
    "storage"
  ],
  "host_permissions": [
    "https://calendar.google.com/*"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "gcal-duplicate-duration@ext.com"
    }
  },
  "icons": {
    "48": "icon48.png",
    "96": "icon96.png"
  },
  "action": {
    "default_title": "GCal Tools",
    "default_popup": "popup.html",
    "default_icon": {
      "48": "icon48.png",
      "96": "icon96.png"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "https://calendar.google.com/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ]
}