Examine source code of Baseliner

{
  "manifest_version": 3,
  "name": "Baseliner",
  "short_name": "Baseliner",
  "description": "Baseliner adds a layer on top of any website with horizontal & vertical lines to help you align your design to a specific baseline.",
  "version": "7.2",
  "author": "J. Pedro Ribeiro",
  "homepage_url": "https://www.jpedroribeiro.com/",
  "action": {
    "default_popup": "index.html",
    "default_title": "Baseliner",
    "default_icon": {
      "16": "icon16.png",
      "48": "icon48.png",
      "128": "icon128.png"
    }
  },
  "icons": {
    "16": "icon16.png",
    "48": "icon48.png",
    "128": "icon128.png"
  },
  "content_security_policy": {
    "extension_pages": "script-src 'self' 'sha256-d8OMhPWLtwxmmPVk+si2J0GiOcDVaPFvC2pJoW/kOlU='; object-src 'self'"
  },
  "permissions": [
    "activeTab",
    "storage",
    "scripting"
  ],
  "web_accessible_resources": [
    {
      "resources": [
        "main.js"
      ],
      "matches": []
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "contact@jpedroribeiro.com"
    }
  }
}