Xaml page code correct but not viewed

Question

Am creating Xaml application code are correct but run on Android  device but only viewed on blank page

how to solve this??????

<StackLayout HorizontalOptions="FillAndExpand">
    <StackLayout.BackgroundColor>
        <OnPlatform x:TypeArguments="Color"
                     Android="#51COD4"
                     iOS="51COD4"
                     WinPhone="51COD4"></OnPlatform>
    </StackLayout.BackgroundColor>
    <ContentPage.BackgroundColor>
        <Label Text="Welcome to Xamarin Forms!"
       VerticalOptions="Center"
       HorizontalOptions="Center" />
<Slider VerticalOptions="FillAndExpand"></Slider>
    </ContentPage.BackgroundColor>

</StackLayout>