Examine source code of Dark mode for Slack

{
  "manifest_version": 2,
  "name": "Slack dark mode",
  "version": "0.2",
  "description": "Icons made by Freepik (https://www.freepik.com/) from https://www.flaticon.com",
  "content_scripts": [
    {
      "matches": [
        "https://*.slack.com/*",
        "http://*.slack.com/*"
      ],
      "js": [
        "content.js"
      ]
    }
  ]
}