The layout for the MainPage is defined in the MainPage.xaml file. This file contains the XAML markup that defines the layout of the application. Replace your MainPage.xaml with the contents below:
<Page x:Class="Counter.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:Counter"
Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
<StackPanel HorizontalAlignment="Center"
VerticalAlignment="Center">
<TextBlock AutomationProperties.AutomationId="HelloTextBlock"
Text="Hello Uno Platform"
HorizontalAlignment="Center" />
</StackPanel>
</Page>