Examine source code of YouTube Zen Mode

{
  "name": "YouTube Zen Mode",
  "version": "2.1.2",
  "description": "Get rid of all the distractions on YouTube",
  "manifest_version": 3,
  "icons": {
    "16": "icons/icon16.png",
    "32": "icons/icon32.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "permissions": [
    "storage",
    "tabs",
    "webNavigation",
    "webRequest"
  ],
  "host_permissions": [
    "*://*.youtube.com/*"
  ],
  "action": {
    "default_popup": "popup.html",
    "default_title": "Zen",
    "default_icon": {
      "16": "icons/icon16.png",
      "32": "icons/icon32.png",
      "48": "icons/icon48.png",
      "128": "icons/icon128.png"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{80b1557a-ec9a-4e6e-8877-8aa4f146c413}"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "https://www.youtube.com/*"
      ],
      "js": [
        "youtube/main.js"
      ],
      "css": [
        "youtube/youtube.css"
      ],
      "run_at": "document_end"
    }
  ]
}