This extension will let Safari fill your entire front screen on an iPhone Duo

As the developer says, Wider will lets page content extend into the space beside Safari's controls on the front screen, simple as that. If you don't want that black bar for browser controls, this will fix that for you. It's free on the App Store, for now.https://www.getwider.app Continue Reading on AppleInsider | Discuss on our Forums

Summary from the AppleInsider feed. The full story lives on their site.