Examine source code of Dark Analog Clock

{
  "manifest_version": 2,
  "name": "Analog Clock",
  "version": "1.1",
  "description": "It's a Dark mode clock.",
  "icons": {
    "512": "clock2.webp"
  },
  "browser_action": {
    "default_popup": "index.html",
    "default_icon": "clock2.webp"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.mozilla.org/*"
      ],
      "js": [
        "clk.js"
      ]
    }
  ]
}