Examine source code of InstaBlack

{
  "manifest_version": 2,
  "name": "instaDark",
  "version": "1.0",
  "description": "Dark mode for instagram.",
  "icons": {
    "48": "icons/icon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.instagram.com/*"
      ],
      "js": [
        "darkinsta.js"
      ]
    }
  ]
}