<Shell.FlyoutHeaderTemplate>
  <DataTemplate>
        <Grid BackgroundColor="Black" HeightRequest="200">
            <Label Text="Shell Hands-on"
                   TextColor="White"
                   FontAttributes="Bold"
                   HorizontalTextAlignment="Center"
                   VerticalTextAlignment="Center" />
        </Grid>
    </DataTemplate>
</Shell.FlyoutHeaderTemplate>
<FlyoutItem Title="Browse">
    <Tab>
        <ShellContent>
            <local:ItemsPage />
        </ShellContent>
    </Tab>
</FlyoutItem>
<FlyoutItem Title="About">
    <Tab>
        <ShellContent>
            <local:AboutPage />
        </ShellContent>
    </Tab>
</FlyoutItem>