Examine source code of Type in White

{
  "manifest_version": 2,
  "name": "fffe",
  "version": "1.0",
  "description": "Changes font color to white on www.typingtest.com",
  "icons": {
    "48": "icon/Paint-Roll-icon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "https://www.typingtest.com/test.html*"
      ],
      "js": [
        "paintitwhite.js"
      ]
    }
  ]
}