I want to know the answer to this checkbox issue in ReactJS

I saw this excellent post: How to get persist checkbox checked on page refresh in React JS?

but when the it came to the answer the link for the answers sandbox was "broken" or disabled... and I really could need a good answer on how they fixed the refresh issue on https://codesandbox.io/s/clever-noether-7ze1r?file=/src/App.js.

if its not to much to ask.