Examine source code of Simple Custom CSS

{
  "name": "Custom CSS",
  "version": "1.0.6",
  "description": "Inject custom CSS in pages",
  "permissions": [
    "storage",
    "activeTab",
    "scripting"
  ],
  "action": {
    "default_popup": "popup.html",
    "default_icon": {
      "48": "icons/favicon.png"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_end",
      "match_about_blank": true,
      "all_frames": true
    }
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "icons": {
    "48": "icons/favicon.png",
    "96": "icons/faviconMiddle.png",
    "128": "icons/faviconBig.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{f363773b-7607-45e8-80c8-aeefbea98e79}",
      "strict_min_version": "58.0"
    }
  },
  "manifest_version": 3
}