Examine source code of Halloween theme

{
  "manifest_version": 2,
  "name": "Halloween theme",
  "version": "1.0",
  "description": "Halloween theme for GitHub",
  "content_scripts": [
    {
      "matches": [
        "*://github.com/*"
      ],
      "js": [
        "halloween-theme.js"
      ]
    }
  ]
}