Examine source code of Dark mode for Substack

{
  "manifest_version": 2,
  "name": "Substack Dark Mode",
  "version": "1.0",
  "description": "Toggle dark mode on Substack articles",
  "permissions": [
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "substack-dark@local",
      "strict_min_version": "109.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ],
        "optional": []
      }
    }
  },
  "browser_action": {
    "default_icon": {
      "48": "icons/icon-48.svg"
    },
    "default_title": "Toggle Substack Dark Mode"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.substack.com/*"
      ],
      "css": [
        "content.css"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_start"
    }
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "commands": {
    "toggle-dark": {
      "suggested_key": {
        "default": "Alt+D"
      },
      "description": "Toggle dark mode"
    }
  },
  "icons": {
    "48": "icons/icon-48.svg"
  }
}