Examine source code of Messenger Dark Theme

{
  "manifest_version": 2,
  "name": "Messenger Dark Theme",
  "author": "Headary",
  "version": "2.1.12",
  "description": "Enable dark mode in inbrowser messenger.",
  "content_scripts": [
    {
      "matches": [
        "*://*.messenger.com/*"
      ],
      "css": [
        "styles.css"
      ],
      "js": [
        "options/inject.js"
      ]
    }
  ],
  "options_ui": {
    "page": "options/options.html"
  },
  "permissions": [
    "storage"
  ],
  "applications": {
    "gecko": {
      "id": "{2c6efd7e-6963-4cd4-b592-68481085db6d}"
    }
  },
  "icons": {
    "32": "icons/32.png",
    "48": "icons/48.png",
    "64": "icons/64.png",
    "96": "icons/96.png",
    "128": "icons/128.png",
    "256": "icons/256.png"
  }
}