Remove in ‘add to home screen’ navigation bar

I have a site in HTML and when I do "add to home screen" from iOS or Android, it remains the navigation bar at the top and doesn't turn like a "web app". I should insert a code string, to make the navigation bar disappear and the ability to access the INTERNET (external pages) I use the "web approval" added to HOME of my Device.

In addition, I would like to know if there was a possibility to "preload" the whole site if the internet didn't work.