Examine source code of Element CSS

{
  "manifest_version": 2,
  "name": "Element",
  "version": "1.0.1",
  "description": "Browser extension based on element css for better html default styles",
  "permissions": [
    "tabs",
    "activeTab",
    "storage",
    "scripting"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "css": [],
      "js": [
        "element.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "icons": {
    "392": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{adef0058-2f1c-4195-b7db-c2f64ab3d771}"
    }
  }
}