Examine source code of Focus Mode: Dim Page

{
  "manifest_version": 2,
  "name": "Focus Mode: Dim Page",
  "version": "1.0.0",
  "description": "Dim the current page to reduce distractions with a single click. Customize intensity in the options.",
  "browser_specific_settings": {
    "gecko": {
      "id": "focus-mode-6cfba09e-3c03-42d7-8bf4-7efd02a5a5ad@example.com"
    }
  },
  "permissions": [
    "activeTab",
    "storage"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_title": "Toggle Focus Mode",
    "default_popup": "popup.html",
    "default_icon": {
      "48": "icons/icon-48.png",
      "128": "icons/icon-128.png"
    }
  },
  "icons": {
    "48": "icons/icon-48.png",
    "128": "icons/icon-128.png"
  },
  "options_ui": {
    "page": "options.html",
    "browser_style": true,
    "open_in_tab": true
  },
  "content_security_policy": "script-src 'self'; object-src 'none';"
}