You can load the page, close it, turn off your internet and open that link again, it should load even when you're offline
If you open the page on a mobile browser, add it to your home screen using a button in your browser and launch it from the home screen, the page will open without the browser UI like a real native app
https://developer.mozilla.org/en-US/docs/Web/API/Service_Worker_API Thanks to @AsyncTheory for bringing this to my attention