Examine source code of Scratch Dark mode

{
  "manifest_version": 2,
  "name": "Scratch Dark mode",
  "version": "0.1",
  "author": "Basha coder",
  "description": "This is an darkmode extension for scratch.",
  "icons": {
    "16": "128.ico",
    "48": "128.ico",
    "128": "128.ico"
  },
  "action": {
    "default_title": "Scratch extension",
    "default_icon": {
      "128": "128.ico"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "https://scratch.mit.edu/*"
      ],
      "js": [
        "script.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{39193184-1111-4d81-a67f-2976b39e8d45}"
    }
  }
}