Examine source code of CSS Breakpoint Button

{
  "manifest_version": 2,
  "name": "CSS Breakpoint Button",
  "homepage_url": "https://css.usefulapps.cloud",
  "description": "A browser extension that displays the current breakpoint for the selected css framework.",
  "default_locale": "en",
  "permissions": [
    "activeTab",
    "storage"
  ],
  "icons": {
    "16": "icons/16.png",
    "19": "icons/19.png",
    "38": "icons/38.png",
    "48": "icons/48.png",
    "96": "icons/96.png",
    "128": "icons/128.png"
  },
  "background": {
    "scripts": [
      "js/background.js"
    ],
    "persistent": false
  },
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "js": [
        "js/content-script.js"
      ]
    }
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_title": "CSS Breakpoint Button",
    "default_icon": {
      "19": "icons/19.png",
      "38": "icons/38.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "webext@divordie.com",
      "strict_min_version": "53.0"
    }
  },
  "version": "0.1.1",
  "content_security_policy": "script-src 'self' ; object-src 'self'"
}