Examine source code of Dark Facebook

{
  "manifest_version": 2,
  "name": "Darker Facebook",
  "version": "0.42",
  "description": "Makes Facebook Darker, easy on the eyes",
  "icons": {
    "48": "icons/dark_facebook-logo.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://www.facebook.com/*"
      ],
      "css": [
        "d_facebook.css"
      ]
    }
  ]
}