WPF rectangle - round just top corners

Question

How can I have just the top corners rounded for a WPF rectange? I created a border and set the CornerRadius property and inside the border I've added my rectangle, but it doesn't work, the rectangle is not rounded.

<Border BorderThickness="1" Grid.Row="0" Grid.ColumnSpan="2" CornerRadius="50,50,0,0" BorderBrush="Black">
 <Rectangle Fill="#FF5A9AE0" Grid.Row="0" Grid.ColumnSpan="2" Stretch="UniformToFill" ClipToBounds="True"/>
</Border>

Answer 1

The problem you've got is that the rectangle is "overflowing" the rounded corners of your border.

A rectangle can't have rounded corners, so if you just put the background colour on the border and remove the rectangle:

<Border BorderThickness="1" Grid.Row="0" Grid.ColumnSpan="2"
        CornerRadius="50,50,0,0" BorderBrush="Black" Background="#FF5A9AE0">
</Border>

You'll get your desired effect.