PP/AlenaTest/Pages/StartPage.xaml

<Page x:Class="AlenaTest.Pages.StartPage"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
      xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
      xmlns:local="clr-namespace:AlenaTest.Pages"
      mc:Ignorable="d" 
      d:DesignHeight="450" d:DesignWidth="800"
      Title="StartPage">
    <!--<Page.Background>
        <ImageBrush ImageSource="/Images/PIC.png"></ImageBrush>
    </Page.Background>-->
    <Grid >
        <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center">
            <Border BorderBrush="Black" BorderThickness="1">
            <TextBlock FontSize="30" Background="White" Text="Профориентационное тестирование" />
            </Border>
            <Button Content="Начать" Click="Button_Click"/>
           
        </StackPanel>
  
    </Grid>
</Page>