New Post: Styling NumericUpDown

<Style TargetType="{x:Type xctk:WatermarkTextBox}">
            <Setter Property="Template" Value="{DynamicResource WatermarkTextBox1}"/>
        </Style>

        <ControlTemplate x:Key="WatermarkTextBox1" TargetType="{x:Type xctk:WatermarkTextBox}">
            <Grid>
                <Border x:Name="Border" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" CornerRadius="1" Opacity="0"/>
                <Border x:Name="MouseOverVisual" BorderThickness="{TemplateBinding BorderThickness}" CornerRadius="1" Opacity="0">
                    <Border.BorderBrush>
                        <LinearGradientBrush EndPoint="0,1" StartPoint="0,0">
                            <GradientStop Color="#FF5794BF" Offset="0.05"/>
                            <GradientStop Color="#FFB7D5EA" Offset="0.07"/>
                            <GradientStop Color="#FFC7E2F1" Offset="1"/>
                        </LinearGradientBrush>
                    </Border.BorderBrush>
                </Border>
                <Border x:Name="FocusVisual" BorderThickness="{TemplateBinding BorderThickness}" CornerRadius="1" Opacity="0">
                    <Border.BorderBrush>
                        <LinearGradientBrush EndPoint="0,1" StartPoint="0,0">
                            <GradientStop Color="#FF3D7BAD" Offset="0.05"/>
                            <GradientStop Color="#FFA4C9E3" Offset="0.07"/>
                            <GradientStop Color="#FFB7D9ED" Offset="1"/>
                        </LinearGradientBrush>
                    </Border.BorderBrush>
                </Border>
                <ScrollViewer x:Name="PART_ContentHost" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                <ContentPresenter x:Name="PART_WatermarkHost" ContentTemplate="{TemplateBinding WatermarkTemplate}" Content="{TemplateBinding Watermark}" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" IsHitTestVisible="False" Margin="{TemplateBinding Padding}" Visibility="Collapsed" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
            </Grid>
            <ControlTemplate.Triggers>
                <MultiTrigger>
                    <MultiTrigger.Conditions>
                        <Condition Property="IsFocused" Value="False"/>
                        <Condition Property="Text" Value=""/>
                    </MultiTrigger.Conditions>
                    <Setter Property="Visibility" TargetName="PART_WatermarkHost" Value="Visible"/>
                </MultiTrigger>
                <Trigger Property="IsMouseOver" Value="True">
                    <Setter Property="Opacity" TargetName="MouseOverVisual" Value="1"/>
                </Trigger>
                <Trigger Property="IsFocused" Value="True">
                    <Setter Property="Opacity" TargetName="FocusVisual" Value="1"/>
                </Trigger>
                <Trigger Property="IsEnabled" Value="False">
                    <Setter Property="BorderBrush" TargetName="Border" Value="#FFADB2B5"/>
                    <Setter Property="Background" TargetName="Border" Value="#FFF4F4F4"/>
                    <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
                    <!--<Setter Property="Opacity" TargetName="Border" Value="0.5"/>-->
                </Trigger>
            </ControlTemplate.Triggers>
        </ControlTemplate>