Examine source code of ChessCom board centerer

{
  "name": "ChessCom board centerer",
  "version": "0.0.4",
  "description": "Centers the board on chess.com, so it's not offset to the left, also available for youtube player",
  "manifest_version": 2,
  "author": "Ville kokkarinen",
  "content_scripts": [
    {
      "css": [
        "styles.css"
      ],
      "js": [
        "BoardCenterer.js",
        "jquery.js"
      ],
      "matches": [
        "https://www.chess.com/*"
      ]
    }
  ],
  "browser_action": {
    "default_popup": "index.html",
    "default_title": "Chess-board-centerer"
  },
  "permissions": [
    "storage",
    "activeTab"
  ],
  "icons": {
    "48": "icons/48.png",
    "96": "icons/96.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{8821f187-69d5-4d67-9365-1516ffd6466f}",
      "strict_min_version": "42.0"
    }
  }
}