Examine source code of Fullscreen HubSpot DM

{
  "manifest_version": 2,
  "name": "Fullscreen HubSpot Design Manager",
  "version": "1.0",
  "description": "Adds a button at the bottom of the hubspot design manager, onclick > fullscreen",
  "icons": {
    "48": "icons/fshs.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://app.hubspot.com/design-manager/*"
      ],
      "js": [
        "script.js"
      ]
    }
  ]
}