& lt grid. ColumnDefinitions & gt
& ltColumnDefinition/>
& ltColumnDefinition/>
& lt/ grid. ColumnDefinitions & gt
& ltEllipse Stroke= "black" panel. ZIndex = " 1 " horizontal alignment = " Stretch " >
& lt/Ellipse & gt;
& lt/Grid & gt;
You divide the grid into two columns, then put Ellipse in one column and set its HorizontalAlignment="Stretch ".