Examine source code of Sandbox Version

{
  "name": "Sandbox Version",
  "short_name": "sandboxver",
  "version": "1.1.1",
  "description": "Shows your sandbox version next to your sandbox host",
  "icons": {
    "16": "icons/icon16.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "author": "Patrick Connelly <patrick@deadlypenguin.com>",
  "permissions": [
    "https://*.salesforce.com/07E*",
    "https://*.force.com/lightning/setup/DataManagementCreateTestInstance/home"
  ],
  "content_scripts": [
    {
      "matches": [
        "https://*.salesforce.com/07E*",
        "https://*.force.com/lightning/setup/DataManagementCreateTestInstance/home"
      ],
      "js": [
        "jquery.min.js",
        "axios.min.js",
        "q.js",
        "content.js"
      ],
      "all_frames": true
    }
  ],
  "manifest_version": 2
}