Examine source code of Overflow Checker

{
  "manifest_version": 3,
  "name": "Scroll Checker",
  "version": "1.0.1",
  "author": "Timothy Popovsky",
  "description": "Adds css styles to each DOM element to make it easier to find the element that causes horizontal scrolling on the site",
  "homepage_url": "https://github.com/Timothy7310/scroll-checker",
  "icons": {
    "16": "./images/icon_16.png",
    "32": "./images/icon_32.png",
    "48": "./images/icon_48.png",
    "128": "./images/icon_128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{a7796221-66df-4f69-9107-90e966cccffb}"
    }
  },
  "action": {
    "default_icon": {
      "16": "./images/icon_16.png",
      "32": "./images/icon_32.png",
      "48": "./images/icon_48.png",
      "128": "./images/icon_128.png"
    },
    "default_popup": "popup.html"
  },
  "permissions": [
    "activeTab",
    "scripting"
  ]
}