Examine source code of scrollable-youtube-side-panel

{
  "manifest_version": 2,
  "name": "modify-page",
  "version": "1.0",
  "content_scripts": [
    {
      "matches": [
        "https://www.youtube.com/*"
      ],
      "js": [
        "scroll.js"
      ]
    }
  ]
}