I set up this repo and used it to turn the "Satoshi Bitcoin Converter" into a PWA.

repo: https://github.com/crrdlx/puredogpwa
SBC: https://satoshibitcoinconverter.com
great template: https://simplepwa.com/

For a PWA, you need to add a few extra things.

1. manifest
2. service worker
3. app icons
4. a few code snippets on pages to make it installable