Please, now disconnect from internet
When you generate your wallets, copy all the data to a safe place and then close this tab, only then turn on the Internet.
This page can work 100% offline.
Buy this offline generatorYou can say that I have prepared a set of private keys on the server and show them now. This is not true, it was generated in your browser. But! I suggest you buy this offline generator, download it to a flash drive and you can always use it in full offline mode.I have been working in the cryptocurrency world for the last few years...
I have never seen a wallet generated anywhere in real offline mode. And if the wallet is generated online, it can always be stolen. For example, on the server, I can substitute a dictionary for a mnemonics only at certain hours of the day (so that you don't notice this over years), change the number of words in the dictionary from 1600 to 16 and then i can brute-force all the generated keys.
Or I can just send data to the server... Anyway many wallets in general directly generate them on the server and send them down through the template engine or API in case SPA applications. Therefore, buy this offline wallet generator for 25$ and be 100% sure that no one else holds your private keys. I hope you do not need to explain why you should not download this generator from torrents and so on :)