Xamarin.android ToggleSoftInput how to make FullScreen?

Question

Android

Hello
, I need to show the software keyboard without losing the full-screen mode when the navigation and status bar are removed from the screen, but something doesn't work. The same thing happens as when calling Dialog or alert - system controls appear. How to avoid it?
here are the pieces of my code

public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsApplicationActivity
{
  public static Activity MyActivity;
  protected override void OnCreate(Bundle bundle)
  {
    base.OnCreate(bundle);
    MyActivity = this; //костыль для имплементации интерфейса, который покажет клавиатуру
    View decorView = Window.DecorView;
    var uiOptions = (int)decorView.SystemUiVisibility;
    int newUiOptions = (int)uiOptions;

    newUiOptions |= (int)SystemUiFlags.LayoutStable;
    newUiOptions |= (int)SystemUiFlags.LayoutHideNavigation;
    newUiOptions |= (int)SystemUiFlags.LayoutFullscreen;

    newUiOptions |= (int)SystemUiFlags.HideNavigation;
    newUiOptions |= (int)SystemUiFlags.Fullscreen;
    newUiOptions |= (int)SystemUiFlags.ImmersiveSticky;

    decorView.SystemUiVisibility = (StatusBarVisibility)newUiOptions;
  // Это переводит приложение в полноэкранный режим, где спрятаны все элементы управления
  }
}

Then I add the implementation of the interface showing the keys in android (and later in ios)

public class CMyKeyboardShower: IMyKeyboardShower
{
  public void ShowKeyboard()
  {
    InputMethodManager inputMethodManager = MainActivity.MyActivity.GetSystemService(Context.InputMethodService) as InputMethodManager;
    inputMethodManager.ToggleSoftInput(ShowFlags.Forced, HideSoftInputFlags.ImplicitOnly);
//клавиатура появляется и возвращает системные элементы экрана
  }
}

In principle, the same thing happens if you just call a dialogue

MainActivity.MyActivity.RunOnUiThread(() =>
{
  var alert = new AlertDialog.Builder(MainActivity.MyActivity);
  alert.SetView(MainActivity.me_act.LayoutInflater.Inflate(Resource.Layout.layout1, null));
  alert.Create().Show();
});

I would be glad for a hint on how to intercept / disable the appearance of system elements
Thank you!
There is an idea that this is impossible due to the fundamental device of the android, but for example, chrome:

Answer 1

h3 {
margin: 0;
}

https://jsfiddle.net/83dnadce/1/

Answer 2

This is how it is done correctly - https://jsfiddle.net/webirus/83dnadce/3/
You need to set normalize.css or reset.css , then you won't have to crutch each indent separately.
Otherwise, the layout will be crooked, and you will get tired of editing in every place.