OnlineMonitorSystem/HandyControl/HandyControl_Shared/Themes/Styles/Base/SplitButtonBaseStyle.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">

    <Style x:Key="SplitButtonBaseStyle" BasedOn="{StaticResource BaseStyle}" TargetType="hc:SplitButton">
        <Setter Property="Height" Value="{StaticResource DefaultControlHeight}"/>
        <Setter Property="BorderBrush" Value="{DynamicResource BorderBrush}"/>
        <Setter Property="Padding" Value="{StaticResource DefaultControlPadding}"/>
        <Setter Property="Foreground" Value="{DynamicResource TextIconBrush}"/>
        <Setter Property="BorderThickness" Value="0"/>
        <Setter Property="HorizontalAlignment" Value="Center"/>
        <Setter Property="VerticalAlignment" Value="Center"/>
        <Setter Property="HorizontalContentAlignment" Value="Center"/>
        <Setter Property="VerticalContentAlignment" Value="Center"/>
        <Setter Property="Background" Value="{DynamicResource RegionBrush}"/>
        <Setter Property="hc:BorderElement.CornerRadius" Value="{StaticResource DefaultCornerRadius}"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="hc:SplitButton">
                    <hc:SimplePanel x:Name="templateRoot">
                        <Border Background="{TemplateBinding Background}" CornerRadius="{Binding Path=(hc:BorderElement.CornerRadius),RelativeSource={RelativeSource TemplatedParent}}"/>
                        <Border BorderThickness="{TemplateBinding BorderThickness}" BorderBrush="{TemplateBinding BorderBrush}" CornerRadius="{Binding Path=(hc:BorderElement.CornerRadius),RelativeSource={RelativeSource TemplatedParent}}">
                            <Grid>
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition/>
                                    <ColumnDefinition Width="Auto"/>
                                </Grid.ColumnDefinitions>
                                <StackPanel Orientation="Horizontal" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}" Margin="{TemplateBinding Padding}">
                                    <Path x:Name="PathMain" Width="{TemplateBinding hc:IconElement.Width}" Height="{TemplateBinding hc:IconElement.Height}" Fill="{TemplateBinding Foreground}" SnapsToDevicePixels="True" Stretch="Uniform" Data="{TemplateBinding hc:IconElement.Geometry}"/>
                                    <ContentPresenter x:Name="ContentPresenterMain" RecognizesAccessKey="True" VerticalAlignment="Center" Margin="6,0,0,0" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                                </StackPanel>
                                <ToggleButton x:Name="PART_Arrow" hc:IconElement.Width="14" Padding="{Binding Padding, RelativeSource={RelativeSource TemplatedParent}, Converter={StaticResource ThicknessSplitConverter}, ConverterParameter='0,1,1,1'}" Foreground="{TemplateBinding Foreground}" IsChecked="{Binding IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}" Height="Auto" Width="Auto" Grid.Column="1" Style="{StaticResource ToggleButtonIconTransparent}" hc:IconSwitchElement.GeometrySelected="{StaticResource UpGeometry}" hc:IconElement.Geometry="{StaticResource DownGeometry}"/>
                            </Grid>
                        </Border>
                        <Popup AllowsTransparency="true" StaysOpen="False" IsOpen="{Binding IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}" Margin="1" PopupAnimation="Fade"  Placement="Bottom">
                            <Border CornerRadius="{Binding Path=(hc:BorderElement.CornerRadius),RelativeSource={RelativeSource TemplatedParent}}" x:Name="dropDownBorder" MaxHeight="{TemplateBinding MaxDropDownHeight}" MinWidth="{Binding ActualWidth, ElementName=templateRoot}" BorderBrush="{DynamicResource BorderBrush}" BorderThickness="1" Background="{DynamicResource RegionBrush}">
                                <ScrollViewer Margin="0,4" x:Name="DropDownScrollViewer">
                                    <hc:SimplePanel RenderOptions.ClearTypeHint="Enabled">
                                        <Canvas HorizontalAlignment="Left" Height="0" VerticalAlignment="Top" Width="0">
                                            <Rectangle x:Name="opaqueRect" Fill="{Binding Background, ElementName=dropDownBorder}" Height="{Binding ActualHeight, ElementName=dropDownBorder}" Width="{Binding ActualWidth, ElementName=dropDownBorder}"/>
                                        </Canvas>
                                        <ContentPresenter ContentSource="DropDownContent"/>
                                    </hc:SimplePanel>
                                </ScrollViewer>
                            </Border>
                        </Popup>
                    </hc:SimplePanel>
                    <ControlTemplate.Triggers>
                        <Trigger Property="Content" Value="{x:Null}">
                            <Setter Property="Visibility" Value="Collapsed" TargetName="ContentPresenterMain"/>
                        </Trigger>
                        <Trigger Property="hc:IconElement.Geometry" Value="{x:Null}">
                            <Setter Property="Visibility" Value="Collapsed" TargetName="PathMain"/>
                            <Setter Property="Margin" Value="0" TargetName="ContentPresenterMain"/>
                        </Trigger>
                        <MultiTrigger>
                            <MultiTrigger.Conditions>
                                <Condition Property="HitMode" Value="Click"/>
                                <Condition Property="IsChecked" Value="True" SourceName="PART_Arrow"/>
                            </MultiTrigger.Conditions>
                            <Setter Property="IsDropDownOpen" Value="True"/>
                        </MultiTrigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
        <Style.Triggers>
            <Trigger Property="IsMouseOver" Value="True">
                <Setter Property="Opacity" Value=".9"/>
            </Trigger>
            <Trigger Property="IsPressed" Value="True">
                <Setter Property="Opacity" Value=".6"/>
            </Trigger>
            <Trigger Property="IsEnabled" Value="False">
                <Setter Property="Opacity" Value="0.4"/>
            </Trigger>
        </Style.Triggers>
    </Style>

</ResourceDictionary>