Como manter a mesma altura e largura das células da grade

Preciso manter oGridltura da célula = largura ao redimensiona

O código de trabalho usando um viewBox:
  <Viewbox>
        <Grid>
            <Grid.RowDefinitions>
                    <RowDefinition Height="1*"/>
                    <RowDefinition Height="1*"/>
                </Grid.RowDefinitions>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="Auto"/>
                    <ColumnDefinition Width="Auto"/>
                </Grid.ColumnDefinitions>
                <Label Grid.Row="0" Grid.Column="0" Background="Black" Width="{Binding RelativeSource={RelativeSource Self}, Path=ActualHeight}"></Label>
                <Label Grid.Row="1" Grid.Column="0" Background="Gray" Width="{Binding RelativeSource={RelativeSource Self}, Path=ActualHeight}"></Label>
                <Label Grid.Row="0" Grid.Column="1" Background="Gray" Width="{Binding RelativeSource={RelativeSource Self}, Path=ActualHeight}"></Label>
                <Label Grid.Row="1" Grid.Column="1" Background="Black" Width="{Binding RelativeSource={RelativeSource Self}, Path=ActualHeight}"></Label>
            </Grid>
        </Viewbox>

Obrigado para H.B. para a ideia de usar um viewBox! :)

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