public Style DecrementButtonStyle { get; set; }

Public Property DecrementButtonStyle As Style

<Window ...
    xmlns:dxe="http://schemas.devexpress.com/winfx/2008/xaml/editors">
    <StackPanel>
        <StackPanel.Resources>
            <Style x:Key="trackBarEditThumbStyle" TargetType="Thumb">
                <Setter Property="Template">
                    <Setter.Value>
                        <ControlTemplate>
                            <Ellipse Width="20" Height="20" Fill="Blue" />
                        </ControlTemplate>
                    </Setter.Value>
                </Setter>
            </Style>
            <Style x:Key="nearTrackStyle" TargetType="RepeatButton">
                <Setter Property="Template">
                    <Setter.Value>
                        <ControlTemplate>
                            <Border Background="#FF6200EE" Height="8"
                                    VerticalAlignment="Center" Margin="0,0,-10,0" CornerRadius="4" />
                        </ControlTemplate>
                    </Setter.Value>
                </Setter>
            </Style>
        </StackPanel.Resources>
            <dxe:TrackBarEdit Margin="5" Minimum="0" Maximum="100" Value="50"
                              Background="#FFDABEFC" BorderBrush="#FFDABEFC"
                              dxe:EditorAppearanceProperties.FocusedBorderBrush="#FFDABEFC"
                              CornerRadius="4" TrackHeight="8" TickPlacement="None" TrackWidth="300"
                              NearTrackStyle="{StaticResource nearTrackStyle}"
                              ThumbStyle="{StaticResource trackBarEditThumbStyle}">
                <dxe:TrackBarEdit.StyleSettings>
                    <dxe:TrackBarZoomStyleSettings DecrementButtonStyle="{StaticResource decrementButtonStyle}"
                                                   IncrementButtonStyle="{StaticResource incrementButtonStyle}" />
                </dxe:TrackBarEdit.StyleSettings>
        </dxe:TrackBarEdit>
    </StackPanel>
</Window>