So to make a Round Corner TextBox , Just Copy The Below Code snippet and paste it where ever you and adjust Grid.Row and Column for Desired position in your Xaml Page,
- <Border Grid.Row="2" Margin="5,50,5,-10" Background="White" BorderBrush="#b7b7b7" BorderThickness="1.5" Width="450" CornerRadius="5">
- <TextBox Height="72" TextWrapping="Wrap" Text="TextBox" Width="456"/>
- </Border>
Comment below for any further Doubts