ScrollBarStyle.xaml

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

    <Style x:Key="ScrollBarLineButtonStyle" TargetType="{x:Type RepeatButton}">
        <Setter Property="Focusable" Value="False"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type RepeatButton}">
                    <Canvas Height="18">
                        <Polygon Fill="{DynamicResource UiElementForegroundAlt}" Points="3,15 15,15 9,3"></Polygon>
                    </Canvas>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

    <Style x:Key="ScrollBarLineButtonBottomStyle" TargetType="{x:Type RepeatButton}">
        <Setter Property="Focusable" Value="False"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type RepeatButton}">
                    <Canvas Height="18">
                        <Polygon Fill="{DynamicResource UiElementForegroundAlt}" Points="3,3 9,15 15,3"></Polygon>
                    </Canvas>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

    <Style x:Key="ScrollBarLineButtonLeftStyle" TargetType="{x:Type RepeatButton}">
        <Setter Property="Focusable" Value="False"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type RepeatButton}">
                    <Canvas Height="18">
                        <Polygon Fill="{DynamicResource UiElementForegroundAlt}" Points="3,9 15,15 15,3"></Polygon>
                    </Canvas>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

    <Style x:Key="ScrollBarLineButtonRightStyle" TargetType="{x:Type RepeatButton}">
        <Setter Property="Focusable" Value="False"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type RepeatButton}">
                    <Canvas Height="18">
                        <Polygon Fill="{DynamicResource UiElementForegroundAlt}" Points="3,3 3,15 15,9"></Polygon>
                    </Canvas>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

    <Style x:Key="ScrollBarPageButtonStyle" TargetType="{x:Type RepeatButton}">
        <Setter Property="IsTabStop" Value="False"/>
        <Setter Property="Focusable" Value="False"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type RepeatButton}">
                    <Border BorderBrush="Transparent"></Border>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

    <Style x:Key="ScrollBarThumbStyle" TargetType="{x:Type Thumb}">
        <Setter Property="IsTabStop" Value="False"/>
        <Setter Property="Focusable" Value="False"/>
        <Setter Property="Margin" Value="1,0,1,0" />
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type Thumb}">
                    <Rectangle Fill="{DynamicResource UiElementForegroundAlt}" Margin="2"></Rectangle>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

    <ControlTemplate x:Key="VerticalScrollBar" TargetType="{x:Type ScrollBar}">
        <Grid>
            <Grid.RowDefinitions>
                <RowDefinition MaxHeight="18"/>
                <RowDefinition Height="*"/>
                <RowDefinition MaxHeight="18"/>
            </Grid.RowDefinitions>

            <RepeatButton Grid.Row="0" Height="18"
                          Style="{StaticResource ScrollBarLineButtonStyle}"
                          Command="ScrollBar.LineUpCommand" >
            </RepeatButton>
            <Track Name="PART_Track" Grid.Row="1" 
                   IsDirectionReversed="True">
                <Track.DecreaseRepeatButton>
                    <RepeatButton Command="ScrollBar.PageUpCommand" Style="{StaticResource ScrollBarPageButtonStyle}">
                    </RepeatButton>
                </Track.DecreaseRepeatButton>
                <Track.Thumb>
                    <Thumb Style="{StaticResource ScrollBarThumbStyle}">
                    </Thumb>
                </Track.Thumb>
                <Track.IncreaseRepeatButton>
                    <RepeatButton Command="ScrollBar.PageDownCommand" Style="{StaticResource ScrollBarPageButtonStyle}">
                    </RepeatButton>
                </Track.IncreaseRepeatButton>
            </Track>
            <RepeatButton Grid.Row="2" Height="18"
                          Style="{StaticResource ScrollBarLineButtonBottomStyle}"
                          Command="ScrollBar.LineDownCommand">
            </RepeatButton>
        </Grid>
    </ControlTemplate>

    <ControlTemplate x:Key="HorizontalScrollBar" TargetType="{x:Type ScrollBar}">
        <Grid>
            <Grid.ColumnDefinitions>
                <ColumnDefinition MaxWidth="18"/>
                <ColumnDefinition Width="0.00001*"/>
                <ColumnDefinition MaxWidth="18"/>
            </Grid.ColumnDefinitions>

            <RepeatButton Grid.Column="0" Width="18"
                          Style="{StaticResource ScrollBarLineButtonLeftStyle}"
                          Command="ScrollBar.LineLeftCommand" >
            </RepeatButton>
            <Track Name="PART_Track" Grid.Column="1" 
                   IsDirectionReversed="False">
                <Track.DecreaseRepeatButton>
                    <RepeatButton Command="ScrollBar.PageLeftCommand" Style="{StaticResource ScrollBarPageButtonStyle}">
                    </RepeatButton>
                </Track.DecreaseRepeatButton>
                <Track.Thumb>
                    <Thumb Style="{StaticResource ScrollBarThumbStyle}">
                    </Thumb>
                </Track.Thumb>
                <Track.IncreaseRepeatButton>
                    <RepeatButton Command="ScrollBar.PageRightCommand" Style="{StaticResource ScrollBarPageButtonStyle}">
                    </RepeatButton>
                </Track.IncreaseRepeatButton>
            </Track>
            <RepeatButton Grid.Column="2" Width="18"
                          Style="{StaticResource ScrollBarLineButtonRightStyle}"
                          Command="ScrollBar.LineRightCommand">
            </RepeatButton>
        </Grid>
    </ControlTemplate>

</ResourceDictionary>