Examine source code of Simple CSS Injector

{
  "manifest_version": 2,
  "name": "Simple CSS Injector",
  "version": "1.0.0",
  "description": "Custom CSS injector with a resizable, dark-themed editor panel and per-domain storage.",
  "author": "Weary Galaxy",
  "icons": {
    "48": "icons/icon-48.png",
    "128": "icons/icon-128.png"
  },
  "browser_action": {
    "default_title": "Open CSS Injector"
  },
  "permissions": [
    "storage",
    "tabs",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content/content-script.js"
      ],
      "css": [
        "content/panel.css"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "simple-css-injector@wearygalaxy",
      "strict_min_version": "58.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}