Rectangle with explicit size and position
<Page xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" HorizontalAlignment="Left" VerticalAlignment="Top"> <Canvas> <Rectangle Fill="Yellow" Stroke="Black" Canvas.Left="30" Canvas.Top="10" Width="100" Height="20" /> </Canvas> </Page>