Как растянуть кнопки на всю ячейку?

<Grid.ColumnDefinitions>
    <ColumnDefinition/>
    <ColumnDefinition/>
</Grid.ColumnDefinitions>

<Grid.RowDefinitions>
    <RowDefinition />
    <RowDefinition />      
</Grid.RowDefinitions>

<StackPanel Grid.Row="1"  Grid.Column="1"      Background="CadetBlue" >
    <Button Name="Ali1" Content="ali0001" VerticalAlignment="Stretch" />
    <Button Name="Ali2" Content="Ali0002" HorizontalAlignment="Stretch" />
 </StackPanel>