Examine source code of Speed Up Whatsapp Audios

{
  "manifest_version": 2,
  "name": "FastAudioWhatsapp",
  "version": "1.2",
  "description": "Change the speed of audios in whatsapp web",
  "homepage": "https://github.com/mateusfg7/FastAudiosWhatsapp",
  "icons": {
    "48": "img/icons/icon_x48.png",
    "60": "img/icons/icon_x60.png",
    "96": "img/icons/icon_x96.png"
  },
  "content_scripts": [
    {
      "matches": [
        "https://web.whatsapp.com/"
      ],
      "js": [
        "index.js"
      ],
      "css": [
        "style.css"
      ]
    }
  ]
}