Examine source code of SimpleYoutube

{
  "manifest_version": 2,
  "name": "SimpleYoutube",
  "version": "0.0.0.1",
  "description": "Get a stressfree youtube experience!",
  "content_scripts": [
    {
      "css": [
        "hide_content.css"
      ],
      "matches": [
        "https://www.youtube.com/*"
      ],
      "run_at": "document_start"
    }
  ]
}