sourcegit/Resources/Styles/ScrollBar.xaml

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

    <Style x:Key="Style.ScrollBar.RepeatPage" TargetType="{x:Type RepeatButton}">
        <Setter Property="SnapsToDevicePixels" Value="True" />
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type RepeatButton}">
                    <Border x:Name="area" Background="Transparent" />

                    <ControlTemplate.Triggers>
                        <Trigger Property="IsMouseOver" Value="True">
                            <Setter TargetName="area" Property="Background" Value="{DynamicResource Brush.FG}" />
                            <Setter TargetName="area" Property="Opacity" Value=".08"/>
                        </Trigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

    <Style x:Key="Style.ScrollBar.Thumb" TargetType="{x:Type Thumb}">
        <Setter Property="Background" Value="{DynamicResource Brush.Border1}" />
        <Setter Property="BorderBrush" Value="Transparent" />
        <Setter Property="BorderThickness" Value="0"/>
        <Setter Property="Focusable" Value="false" />
        <Setter Property="IsTabStop" Value="false" />
        <Setter Property="SnapsToDevicePixels" Value="true" />
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type Thumb}">
                    <Border x:Name="Border" Background="{TemplateBinding Background}"
                            BorderBrush="{TemplateBinding BorderBrush}"
                            BorderThickness="{TemplateBinding BorderThickness}"
                            Opacity=".6"/>
                    <ControlTemplate.Triggers>
                        <Trigger Property="IsMouseOver" Value="True">
                            <Setter TargetName="Border" Property="Opacity" Value="1" />
                        </Trigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

    <ControlTemplate x:Key="Template.ScrollBar.Horizontal" TargetType="{x:Type ScrollBar}">
        <Grid>
            <Track Name="PART_Track" Grid.Column="1">
                <Track.DecreaseRepeatButton>
                    <RepeatButton Command="ScrollBar.PageLeftCommand" Style="{StaticResource Style.ScrollBar.RepeatPage}" />
                </Track.DecreaseRepeatButton>
                <Track.Thumb>
                    <Thumb Style="{StaticResource Style.ScrollBar.Thumb}" />
                </Track.Thumb>
                <Track.IncreaseRepeatButton>
                    <RepeatButton Command="ScrollBar.PageRightCommand" Style="{StaticResource Style.ScrollBar.RepeatPage}" />
                </Track.IncreaseRepeatButton>
            </Track>
        </Grid>
    </ControlTemplate>

    <ControlTemplate x:Key="Template.ScrollBar.Vertical" TargetType="{x:Type ScrollBar}">
        <Grid>
            <Track Name="PART_Track"
                   Grid.Row="1"
                   IsDirectionReversed="true">
                <Track.DecreaseRepeatButton>
                    <RepeatButton Command="ScrollBar.PageUpCommand" Style="{StaticResource Style.ScrollBar.RepeatPage}" />
                </Track.DecreaseRepeatButton>
                <Track.Thumb>
                    <Thumb Style="{StaticResource Style.ScrollBar.Thumb}"/>
                </Track.Thumb>
                <Track.IncreaseRepeatButton>
                    <RepeatButton Command="ScrollBar.PageDownCommand" Style="{StaticResource Style.ScrollBar.RepeatPage}" />
                </Track.IncreaseRepeatButton>
            </Track>
        </Grid>
    </ControlTemplate> 
    
    <Style TargetType="{x:Type ScrollBar}">
        <Setter Property="SnapsToDevicePixels" Value="True"/>
        <Setter Property="OverridesDefaultStyle" Value="True"/>
        <Setter Property="Background" Value="Transparent"/>

        <Style.Triggers>
            <Trigger Property="Orientation" Value="Vertical">
                <Setter Property="Height" Value="Auto" />
                <Setter Property="Template" Value="{StaticResource Template.ScrollBar.Vertical}" />
                <Setter Property="Width" Value="8" />
            </Trigger>
            <Trigger Property="Orientation" Value="Horizontal">
                <Setter Property="Height" Value="8" />
                <Setter Property="Template" Value="{StaticResource Template.ScrollBar.Horizontal}" />
                <Setter Property="Width" Value="Auto" />
            </Trigger>
        </Style.Triggers>
    </Style>
</ResourceDictionary>