So what? It is mentionned in the introduction that it is meant for computer users:
"What do I need?
You need a computer with internet access. I wrote this book in a generic way so that it would be applicable for people using macOS, Windows, or Linux. If I point you toward software to install, it will be free (or have a usable free tier) and will be cross-platform (or I will offer platform alternatives)."
https://htmlforpeople.com/intro/#what-do-i-need%3F
"What do I need?
You need a computer with internet access. I wrote this book in a generic way so that it would be applicable for people using macOS, Windows, or Linux. If I point you toward software to install, it will be free (or have a usable free tier) and will be cross-platform (or I will offer platform alternatives)." https://htmlforpeople.com/intro/#what-do-i-need%3F