<TextBox x:Name="firstName" Validation.Error="Text_ValidationError"
                 Text="{Binding UpdateSourceTrigger=LostFocus, Path=firstName, ValidatesOnDataErrors=true, NotifyOnValidationError=true}" Margin="30,12,50,245" FontSize="32">
            <TextBox.Style>
                <Style TargetType="TextBox">
                    <Style.Triggers>
                        <Trigger Property="Text" Value="">
                            <Setter Property="Background">
                                <Setter.Value>
                                    <VisualBrush Stretch="None">
                                        <VisualBrush.Visual>
                                            <TextBlock FontSize="32" Foreground="Gray" >First Name</TextBlock>
                                        </VisualBrush.Visual>
                                    </VisualBrush>
                                </Setter.Value>
                            </Setter>
                        </Trigger>
                    </Style.Triggers>
                </Style>
            </TextBox.Style>
        </TextBox>