Examine source code of HellSite

{
  "browser_specific_settings": {
    "gecko": {
      "id": "alex465465@gmail.com"
    }
  },
  "manifest_version": 3,
  "name": "HellSite",
  "version": "1.0.0",
  "description": "Extension Description",
  "action": {
    "default_icon": "assets/3x.png"
  },
  "icons": {
    "16": "assets/1x.png",
    "48": "assets/2x.png",
    "128": "assets/3x.png"
  },
  "content_scripts": [
    {
      "matches": [
        "https://progtest.fit.cvut.cz/*"
      ],
      "css": [
        "styles.css"
      ]
    }
  ]
}