Examine source code of Clock Background

{
  "manifest_version": 2,
  "name": "Clock Background",
  "version": "1.0",
  "description": "A clock with a dinamically background image and weather temperature status.",
  "icons": {
    "16": "./assets/icon16.png",
    "48": "./assets/icon48.png",
    "128": "./assets/icon128.png",
    "192": "./assets/icon192.png"
  },
  "page_action": {
    "default_popup": "index.html",
    "default_icon": "./assets/icon16.png",
    "default_title": "Clock Background"
  },
  "chrome_url_overrides": {
    "newtab": "index.html"
  },
  "permissions": [
    "tabs",
    "storage"
  ]
}