Examine source code of LunaNotes

{
  "version": "1.3.9",
  "name": "LunaNotes",
  "short_name": "LunaNotes",
  "description": "LunaNotes - Take notes on YouTube",
  "author": "jfdelarosa",
  "externally_connectable": {
    "matches": [
      "http://*.localhost:*/*",
      "https://*.lunanotes.io/*"
    ]
  },
  "background": {
    "scripts": [
      "background/index.js"
    ],
    "persistent": false
  },
  "default_locale": "en",
  "icons": {
    "128": "assets/icon.png"
  },
  "manifest_version": 2,
  "content_scripts": [
    {
      "matches": [
        "https://*.youtube.com/*"
      ],
      "js": [
        "content/content.js"
      ],
      "css": [
        "assets/styles.css",
        "content/style.css"
      ],
      "run_at": "document_start"
    }
  ],
  "web_accessible_resources": [
    "assets/*",
    "content/style.css",
    "assets/styles.css"
  ],
  "permissions": [
    "storage",
    "https://*.youtube.com/*",
    "http://*.localhost:*/*",
    "https://*.lunanotes.io/*"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{195ac93d-b38d-4a55-8bab-9e0b8dd07c98}"
    }
  }
}