Examine source code of Dark Theme Switcher

{
  "manifest_version": 3,
  "name": "Dark Theme Switcher",
  "version": "1.0.0",
  "description": "Toggle dark theme for backorder.ru and expired.ru websites",
  "browser_specific_settings": {
    "gecko": {
      "id": "kopoba.webmaster@gmail.com"
    }
  },
  "icons": {
    "16": "icons/icon16.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icons/icon16.png",
      "48": "icons/icon48.png",
      "128": "icons/icon128.png"
    }
  },
  "permissions": [
    "storage",
    "activeTab"
  ],
  "host_permissions": [
    "*://*.backorder.ru/*",
    "*://*.expired.ru/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://*.backorder.ru/*",
        "*://*.expired.ru/*"
      ],
      "js": [
        "browser-polyfill.js",
        "content.js"
      ],
      "run_at": "document_start",
      "all_frames": true
    }
  ],
  "background": {
    "service_worker": "background-worker.js",
    "scripts": [
      "browser-polyfill.js",
      "background.js"
    ]
  },
  "web_accessible_resources": [
    {
      "resources": [
        "css/backorder.css",
        "css/expired.css"
      ],
      "matches": [
        "*://*.backorder.ru/*",
        "*://*.expired.ru/*"
      ]
    }
  ]
}