Examine source code of Dark Mode Detox

{
  "manifest_version": 3,
  "name": "__MSG_extensionName__",
  "version": "1.0",
  "description": "__MSG_extensionDescription__",
  "icons": {
    "128": "icons/icon128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{150d304d-11e9-1390-2b10-25aaa351ab46}"
    }
  },
  "permissions": [
    "storage",
    "scripting",
    "activeTab"
  ],
  "host_permissions": [
    "*://*.facebook.com/*",
    "*://*.twitter.com/*",
    "*://*.instagram.com/*"
  ],
  "action": {
    "default_popup": "popup/popup.html",
    "default_icon": {
      "128": "icons/icon128.png"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.facebook.com/*",
        "*://*.twitter.com/*",
        "*://*.instagram.com/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_start"
    }
  ]
}