Examine source code of CodewarsKatana

{
  "manifest_version": 2,
  "name": "CodewarsKatana",
  "description": "This extension brings small improvements to codewars.com.",
  "version": "0.1.2",
  "browser_action": {
    "default_icon": "/images/icon.png"
  },
  "icons": {
    "64": "/images/icon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "https://www.codewars.com/*",
        "http://codewars.com/*"
      ],
      "js": [
        "index.js"
      ],
      "css": [
        "/css/styles.css"
      ]
    }
  ]
}