<meta name="viewport" content="width=device-width, initial-scale=1">

Question

what is the meaning the code above ? Then , which programme have this code ? javascript ? html or css ???

Answer 1

This looks like the metadata of bootstrap 3.
Check out these web codes made with bootstrap.
https://code.sololearn.com/WMoE618WMolH/?ref=app
https://code.sololearn.com/WG4QYkInn4nS/?ref=app

Answer 2

ok . so this in turn means that every html pages need to add <meta > element inside there ???