Examine source code of GDark: Dark mode for Gmail & Chat

{
  "manifest_version": 3,
  "name": "GDark: Dark mode for Gmail & Chat",
  "version": "2.4.0",
  "description": "Darkens the white email pane and reply box that Gmail's dark theme leaves bright. Nothing else changes. Optional night schedule.",
  "icons": {
    "16": "icons/icon-16.png",
    "32": "icons/icon-32.png",
    "48": "icons/icon-48.png",
    "64": "icons/icon-64.png",
    "96": "icons/icon-96.png",
    "128": "icons/icon-128.png"
  },
  "permissions": [
    "storage"
  ],
  "action": {
    "default_title": "GDark — dark mode for Gmail & Chat",
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icons/icon-16.png",
      "32": "icons/icon-32.png"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "https://mail.google.com/*",
        "https://chat.google.com/*"
      ],
      "css": [
        "darkbox.css"
      ],
      "js": [
        "gate.js"
      ],
      "run_at": "document_start",
      "all_frames": true
    },
    {
      "matches": [
        "https://mail.google.com/*"
      ],
      "exclude_matches": [
        "https://mail.google.com/chat/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle",
      "all_frames": true
    },
    {
      "matches": [
        "https://mail.google.com/chat/*",
        "https://chat.google.com/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_start",
      "all_frames": true
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "gmail-darkbox@texs.org",
      "strict_min_version": "127.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}