HandyControl/src/Shared/HandyControl_Shared/Themes/Styles/ScrollViewer.xaml

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:hc="clr-namespace:HandyControl.Controls"
                    xmlns:themes="clr-namespace:HandyControl.Themes">

    <ResourceDictionary.MergedDictionaries>
        <themes:SharedResourceDictionary Source="pack://application:,,,/HandyControl;component/Themes/Styles/Base/ScrollViewerBaseStyle.xaml"/>
        <themes:SharedResourceDictionary Source="pack://application:,,,/HandyControl;component/Themes/Basic/Converters.xaml"/>
        <themes:SharedResourceDictionary Source="pack://application:,,,/HandyControl;component/Themes/Basic/Geometries.xaml"/>
        <themes:SharedResourceDictionary Source="pack://application:,,,/HandyControl;component/Themes/Styles/RepeatButton.xaml"/>
    </ResourceDictionary.MergedDictionaries>

    <!--default style-->
    <Style BasedOn="{StaticResource ScrollViewerNativeBaseStyle}" TargetType="ScrollViewer"/>

    <Style BasedOn="{StaticResource ScrollViewerBaseStyle}" TargetType="hc:ScrollViewer"/>

    <Style x:Key="ScrollViewerUpDownRepeatButtonStyle" BasedOn="{StaticResource RepeatButtonIcon}" TargetType="RepeatButton">
        <Setter Property="HorizontalAlignment" Value="Stretch"/>
        <Setter Property="Height" Value="10"/>
        <Setter Property="Padding" Value="0,2"/>
        <Setter Property="Foreground" Value="{DynamicResource PrimaryTextBrush}"/>
        <Setter Property="ClickMode" Value="Hover"/>
    </Style>
    
    <ControlTemplate x:Key="ScrollViewerUpDownControlTemplate" TargetType="ScrollViewer">
        <Grid x:Name="Grid" Background="{TemplateBinding Background}">
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto"/>
                <RowDefinition/>
                <RowDefinition Height="Auto"/>
            </Grid.RowDefinitions>
            <RepeatButton Style="{StaticResource ScrollViewerUpDownRepeatButtonStyle}" hc:IconElement.Geometry="{StaticResource UpGeometry}" CommandTarget="{Binding RelativeSource={RelativeSource TemplatedParent}}" Command="{x:Static ScrollBar.LineUpCommand}">
                <RepeatButton.Visibility>
                    <MultiBinding FallbackValue="Visibility.Collapsed" Converter="{StaticResource MenuScrollingVisibilityConverter}" ConverterParameter="0">
                        <Binding RelativeSource="{RelativeSource TemplatedParent}" Path="ComputedVerticalScrollBarVisibility" />
                        <Binding RelativeSource="{RelativeSource TemplatedParent}" Path="VerticalOffset" />
                        <Binding RelativeSource="{RelativeSource TemplatedParent}" Path="ExtentHeight" />
                        <Binding RelativeSource="{RelativeSource TemplatedParent}" Path="ViewportHeight" />
                    </MultiBinding>
                </RepeatButton.Visibility>
            </RepeatButton>
            <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="1"/>
            <RepeatButton Style="{StaticResource ScrollViewerUpDownRepeatButtonStyle}" hc:IconElement.Geometry="{StaticResource DownGeometry}" CommandTarget="{Binding RelativeSource={RelativeSource TemplatedParent}}" Grid.Row="2" Command="{x:Static ScrollBar.LineDownCommand}">
                <RepeatButton.Visibility>
                    <MultiBinding FallbackValue="Visibility.Collapsed" Converter="{StaticResource MenuScrollingVisibilityConverter}" ConverterParameter="100">
                        <Binding RelativeSource="{RelativeSource TemplatedParent}" Path="ComputedVerticalScrollBarVisibility" />
                        <Binding RelativeSource="{RelativeSource TemplatedParent}" Path="VerticalOffset" />
                        <Binding RelativeSource="{RelativeSource TemplatedParent}" Path="ExtentHeight" />
                        <Binding RelativeSource="{RelativeSource TemplatedParent}" Path="ViewportHeight" />
                    </MultiBinding>
                </RepeatButton.Visibility>
            </RepeatButton>
        </Grid>
    </ControlTemplate>
    
    <Style x:Key="ScrollViewerUpDown" TargetType="ScrollViewer">
        <Setter Property="VerticalScrollBarVisibility" Value="Auto"/>
        <Setter Property="Focusable" Value="False"/>
        <Setter Property="Template" Value="{StaticResource ScrollViewerUpDownControlTemplate}"/>
    </Style>

</ResourceDictionary>