Examine source code of clean-duck

{
  "manifest_version": 2,
  "name": "clean-duck",
  "version": "1.1",
  "description": "remove logo and text below search bar.",
  "content_scripts": [
    {
      "matches": [
        "*://*.duckduckgo.com/"
      ],
      "js": [
        "clean.js"
      ],
      "css": [
        "clean.css"
      ]
    }
  ]
}