HandyControl/src/Avalonia/HandyControl_Avalonia/Themes/Styles/ScrollBar.axaml

<ResourceDictionary xmlns="https://github.com/avaloniaui"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <ControlTheme x:Key="{x:Type ScrollBar}"
                  TargetType="ScrollBar">
        <Setter Property="Cursor"
                Value="Arrow" />

        <Style Selector="^:horizontal">
            <Setter Property="Height"
                    Value="{DynamicResource ScrollBarThickness}" />
            <Setter Property="Template">
                <ControlTemplate>
                    <Border Background="{DynamicResource ThemeControlMidBrush}"
                            UseLayoutRounding="False">
                        <Grid ColumnDefinitions="Auto,*,Auto"
                              RowDefinitions="*,*,*">
                            <RepeatButton Name="PART_LineUpButton"
                                          Grid.Row="0"
                                          Grid.Column="0"
                                          MinWidth="{DynamicResource ScrollBarThickness}"
                                          VerticalAlignment="Center"
                                          Classes="repeat"
                                          Focusable="False">
                                <Path Data="M 4 0 L 4 8 L 0 4 Z" />
                            </RepeatButton>
                            <Track Grid.Row="1"
                                   Grid.Column="1"
                                   Maximum="{TemplateBinding Maximum}"
                                   Minimum="{TemplateBinding Minimum}"
                                   Orientation="{TemplateBinding Orientation}"
                                   ViewportSize="{TemplateBinding ViewportSize}"
                                   DeferThumbDrag="{TemplateBinding ScrollViewer.IsDeferredScrollingEnabled}"
                                   Value="{TemplateBinding Value,
                                             Mode=TwoWay}">
                                <Track.DecreaseButton>
                                    <RepeatButton Name="PART_PageUpButton"
                                                  Classes="repeattrack"
                                                  Focusable="False" />
                                </Track.DecreaseButton>
                                <Track.IncreaseButton>
                                    <RepeatButton Name="PART_PageDownButton"
                                                  Classes="repeattrack"
                                                  Focusable="False" />
                                </Track.IncreaseButton>
                                <Thumb Name="thumb" />
                            </Track>
                            <RepeatButton Name="PART_LineDownButton"
                                          Grid.Row="2"
                                          Grid.Column="2"
                                          MinWidth="{DynamicResource ScrollBarThickness}"
                                          VerticalAlignment="Center"
                                          Classes="repeat"
                                          Focusable="False">
                                <Path Data="M 0 0 L 4 4 L 0 8 Z" />
                            </RepeatButton>
                        </Grid>
                    </Border>
                </ControlTemplate>
            </Setter>
        </Style>
        <Style Selector="^:vertical">
            <Setter Property="Width"
                    Value="{DynamicResource ScrollBarThickness}" />
            <Setter Property="Template">
                <ControlTemplate>
                    <Border Background="{DynamicResource ThemeControlMidBrush}"
                            UseLayoutRounding="False">
                        <Grid RowDefinitions="Auto,*,Auto">
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition />
                                <ColumnDefinition />
                                <ColumnDefinition />
                            </Grid.ColumnDefinitions>
                            <RepeatButton Name="PART_LineUpButton"
                                          Grid.Row="0"
                                          MinHeight="{DynamicResource ScrollBarThickness}"
                                          HorizontalAlignment="Center"
                                          Classes="repeat"
                                          Focusable="False">
                                <Path Data="M 0 4 L 8 4 L 4 0 Z" />
                            </RepeatButton>
                            <Track Grid.Row="1"
                                   Grid.Column="1"
                                   IsDirectionReversed="True"
                                   Maximum="{TemplateBinding Maximum}"
                                   Minimum="{TemplateBinding Minimum}"
                                   Orientation="{TemplateBinding Orientation}"
                                   ViewportSize="{TemplateBinding ViewportSize}"
                                   DeferThumbDrag="{TemplateBinding ScrollViewer.IsDeferredScrollingEnabled}"
                                   Value="{TemplateBinding Value,
                                             Mode=TwoWay}">
                                <Track.DecreaseButton>
                                    <RepeatButton Name="PART_PageUpButton"
                                                  Classes="repeattrack"
                                                  Focusable="False" />
                                </Track.DecreaseButton>
                                <Track.IncreaseButton>
                                    <RepeatButton Name="PART_PageDownButton"
                                                  Classes="repeattrack"
                                                  Focusable="False" />
                                </Track.IncreaseButton>
                                <Thumb Name="thumb" />
                            </Track>
                            <RepeatButton Name="PART_LineDownButton"
                                          Grid.Row="2"
                                          Grid.Column="2"
                                          MinHeight="{DynamicResource ScrollBarThickness}"
                                          HorizontalAlignment="Center"
                                          Classes="repeat"
                                          Focusable="False">
                                <Path Data="M 0 0 L 4 4 L 8 0 Z" />
                            </RepeatButton>
                        </Grid>
                    </Border>
                </ControlTemplate>
            </Setter>
        </Style>
        <Style Selector="^ /template/ Thumb#thumb">
            <Setter Property="Background"
                    Value="{DynamicResource ThemeControlMidHighBrush}" />
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate>
                        <Border Background="{TemplateBinding Background}" />
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
        <Style Selector="^ /template/ Thumb#thumb:pointerover">
            <Setter Property="Background"
                    Value="{DynamicResource ThemeControlHighBrush}" />
        </Style>
        <Style Selector="^ /template/ Thumb#thumb:pressed">
            <Setter Property="Background"
                    Value="{DynamicResource ThemeControlVeryHighBrush}" />
        </Style>
        <Style Selector="^:horizontal /template/ Thumb#thumb">
            <Setter Property="MinWidth"
                    Value="{DynamicResource ScrollBarThickness}" />
            <Setter Property="Height"
                    Value="{DynamicResource ScrollBarThumbThickness}" />
        </Style>
        <Style Selector="^:vertical /template/ Thumb#thumb">
            <Setter Property="MinHeight"
                    Value="{DynamicResource ScrollBarThickness}" />
            <Setter Property="Width"
                    Value="{DynamicResource ScrollBarThumbThickness}" />
        </Style>
        <Style Selector="^ /template/ RepeatButton.repeat">
            <Setter Property="Padding"
                    Value="2" />
            <Setter Property="BorderThickness"
                    Value="0" />
        </Style>
        <Style Selector="^ /template/ RepeatButton.repeattrack">
            <Setter Property="Template">
                <ControlTemplate>
                    <Border Background="{TemplateBinding Background}" />
                </ControlTemplate>
            </Setter>
        </Style>

        <Style Selector="^ /template/ RepeatButton > Path">
            <Setter Property="Fill"
                    Value="{DynamicResource ThemeForegroundLowBrush}" />
        </Style>

        <Style Selector="^ /template/ RepeatButton:pointerover > Path">
            <Setter Property="Fill"
                    Value="{DynamicResource ThemeAccentBrush}" />
        </Style>
    </ControlTheme>
</ResourceDictionary>