In WPF, how to customize the style of ScrollBar in ScrollViewer - wpf

Question

I can add a ScrollBar style as global. But that will alse change all the ScrollBar except in ScrollViewer.
How can I just change the style of ScrollBar in ScrollViewer. Maybe add a style with a Key and specify it to somewhere like a ControlTemplate.
Here is my fully ScrollBar style:
<Style x:Key="ScrollBarThumb" TargetType="{x:Type Thumb}">
<Setter Property="OverridesDefaultStyle" Value="true"/>
<Setter Property="IsTabStop" Value="false"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type Thumb}">
<Border x:Name="rectangle"
SnapsToDevicePixels="True"
Background="{StaticResource WordBlueBrush}"
Opacity="0.3"
CornerRadius="4"
Height="{TemplateBinding Height}"
Width="{TemplateBinding Width}"/>
<ControlTemplate.Triggers>
<Trigger Property="IsMouseOver" Value="true">
<Setter TargetName="rectangle" Property="Opacity" Value="1" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<Style TargetType="{x:Type ScrollBar}">
<Setter Property="Stylus.IsPressAndHoldEnabled" Value="false"/>
<Setter Property="Stylus.IsFlicksEnabled" Value="false"/>
<Setter Property="Width" Value="14"/>
<Setter Property="Margin" Value="-14 0 0 0" />
<Setter Property="MinWidth" Value="{Binding Height, RelativeSource={RelativeSource Self}}"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ScrollBar}">
<Grid x:Name="Bg" SnapsToDevicePixels="true">
<Border Padding="0 4">
<Track x:Name="PART_Track"
IsDirectionReversed="true"
IsEnabled="{TemplateBinding IsMouseOver}"
Width="8"
HorizontalAlignment="Center"
>
<Track.DecreaseRepeatButton>
<RepeatButton Opacity="0" Command="{x:Static ScrollBar.PageUpCommand}" />
</Track.DecreaseRepeatButton>
<Track.IncreaseRepeatButton>
<RepeatButton Opacity="0" Command="{x:Static ScrollBar.PageDownCommand}" />
</Track.IncreaseRepeatButton>
<Track.Thumb>
<Thumb Style="{StaticResource ScrollBarThumb }" />
</Track.Thumb>
</Track>
</Border>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>

Answer 1

Finally, I got my solution.
1st, add a key to the ScrollBar style:
<Style x:Key="ViewerScrollBar" TargetType="{x:Type ScrollBar}">
2nd, right click the ScrollViewer in Visual Studio XAML Designer. Chose 'Edit Template'->'Edit a Copy':
Add ControlTemplate for ScrollViewer
3rd, in the 'Create Style Resource' dialog, specify a key for the ScrollViewer style and click 'OK':
Create Style Resource Dialog
4th, Visual Studio will automatically create the ControlTemplate for my ScrollViewer. Now, add Style="{StaticResource ViewerScrollBar}" for the horizontal ScrollBar and verticalScrollBar:
<ControlTemplate x:Key="ScrollViewerControlTemplate" TargetType="{x:Type ScrollViewer}">
<Grid x:Name="Grid" Background="{TemplateBinding Background}">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="Auto"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="*"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<Rectangle x:Name="Corner" Grid.Column="1" Fill="{DynamicResource {x:Static SystemColors.ControlBrushKey}}" Grid.Row="1"/>
<ScrollContentPresenter x:Name="PART_ScrollContentPresenter" CanContentScroll="{TemplateBinding CanContentScroll}" CanHorizontallyScroll="False" CanVerticallyScroll="False" ContentTemplate="{TemplateBinding ContentTemplate}" Content="{TemplateBinding Content}" Grid.Column="0" Margin="{TemplateBinding Padding}" Grid.Row="0"/>
<ScrollBar Style="{StaticResource ViewerScrollBar}" x:Name="PART_VerticalScrollBar" AutomationProperties.AutomationId="VerticalScrollBar" Cursor="Arrow" Grid.Column="1" Maximum="{TemplateBinding ScrollableHeight}" Minimum="0" Grid.Row="0" Visibility="{TemplateBinding ComputedVerticalScrollBarVisibility}" Value="{Binding VerticalOffset, Mode=OneWay, RelativeSource={RelativeSource TemplatedParent}}" ViewportSize="{TemplateBinding ViewportHeight}"/>
<ScrollBar Style="{StaticResource ViewerScrollBar}" x:Name="PART_HorizontalScrollBar" AutomationProperties.AutomationId="HorizontalScrollBar" Cursor="Arrow" Grid.Column="0" Maximum="{TemplateBinding ScrollableWidth}" Minimum="0" Orientation="Horizontal" Grid.Row="1" Visibility="{TemplateBinding ComputedHorizontalScrollBarVisibility}" Value="{Binding HorizontalOffset, Mode=OneWay, RelativeSource={RelativeSource TemplatedParent}}" ViewportSize="{TemplateBinding ViewportWidth}"/>
</Grid>
</ControlTemplate>