------------------------------------------------TextBox Style------------------------------------------------

<Style x:Key="WatermarkTextBox" BasedOn="{StaticResource ControlStyle}" TargetType="{x:Type TextBox}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type TextBox}">
                <Grid>
                    <Border x:Name="BorderBase" Background="White" BorderThickness="1.4,1.4,1,1" BorderBrush="Silver">
                        <Label x:Name="TextPrompt" 
                            Content="{Binding RelativeSource={RelativeSource  Mode=TemplatedParent}, Path=Tag}" 
                            Background="{TemplateBinding Background}" Visibility="Collapsed" 
                            Focusable="False" Foreground="Silver"/>
                    </Border>
                    <ScrollViewer Margin="0" x:Name="PART_ContentHost" Foreground="Black"/>
                </Grid>
                <ControlTemplate.Triggers>
                    <MultiTrigger>
                        <MultiTrigger.Conditions>
                            <Condition Property="IsFocused" Value="False"/>
                            <Condition Property="Text" Value=""/>
                        </MultiTrigger.Conditions>
                        <Setter Property="Visibility" TargetName="TextPrompt" Value="Visible"/>
                    </MultiTrigger>
                    <Trigger Property="IsEnabled" Value="False">
                        <Setter Property="Foreground" Value="DimGray" />
                    </Trigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>
       
------------------------------------------------TextBox------------------------------------------------

<TextBox Grid.Row="1" Text="{Binding Login}" Style="{StaticResource WatermarkTextBox}" Tag="Full Name" />