Examine source code of No GitHub Dark Mode

{
  "name": "No GitHub Dark Mode",
  "version": "2.0.2",
  "description": "Bring back the old GitHub menu bar.",
  "manifest_version": 2,
  "browser_specific_settings": {
    "gecko": {
      "id": "no-github-dark-mode@gluons.github.io",
      "strict_min_version": "52.0"
    }
  },
  "author": "Saran Tanpituckpong",
  "homepage_url": "https://github.com/gluons/NoGithubDarkMode-Firefox",
  "icons": {
    "48": "icon/github-logo.svg",
    "96": "icon/github-logo.svg"
  },
  "permissions": [
    "https://github.com/*",
    "https://gist.github.com/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "https://github.com/*",
        "https://gist.github.com/*"
      ],
      "run_at": "document_start",
      "css": [
        "./NoDarkMode.css"
      ]
    }
  ]
}