Examine source code of Fancyground

{
  "manifest_version": 2,
  "name": "Fancyground",
  "version": "1.3.0",
  "description": "Custom arrows and square highlights for lichess.org.",
  "author": "Albert Ford",
  "homepage_url": "https://github.com/370417/fancyground",
  "permissions": [
    "storage"
  ],
  "icons": {
    "48": "icons/icon@48.png",
    "128": "icons/icon@128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "https://lichess.org/*"
      ],
      "js": [
        "bundled/index.js"
      ],
      "css": [
        "static/index.css"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "fancyground@albertford.com"
    }
  },
  "options_ui": {
    "page": "static/options.html"
  },
  "page_action": {
    "default_icon": "icons/icon@48.png",
    "default_popup": "static/options.html",
    "default_title": "Fancyground",
    "show_matches": [
      "https://lichess.org/*"
    ]
  }
}