HandyControl/src/Shared/HandyControl_Shared/Themes/Styles/Base/ProgressButtonBaseStyle.xaml

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:controls="clr-namespace:HandyControl.Controls"
                    xmlns:themes="clr-namespace:HandyControl.Themes">

    <ResourceDictionary.MergedDictionaries>
        <themes:SharedResourceDictionary Source="pack://application:,,,/HandyControl;component/Themes/Styles/Base/ToggleButtonBaseStyle.xaml"/>
        <themes:SharedResourceDictionary Source="pack://application:,,,/HandyControl;component/Themes/Styles/Base/ProgressBarBaseStyle.xaml"/>
    </ResourceDictionary.MergedDictionaries>

    <Style x:Key="ProgressBarFlat4ProgressButton" TargetType="ProgressBar">
        <Setter Property="Background" Value="Transparent"/>
        <Setter Property="controls:BorderElement.CornerRadius" Value="{StaticResource DefaultCornerRadius}"/>
        <Setter Property="Foreground" Value="{DynamicResource DarkMaskBrush}"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="ProgressBar">
                    <Border x:Name="PART_Track">
                        <Decorator x:Name="PART_Indicator" HorizontalAlignment="Left">
                            <Border CornerRadius="{Binding Path=(controls:BorderElement.CornerRadius),RelativeSource={RelativeSource TemplatedParent}}" x:Name="Indicator" Background="{TemplateBinding Foreground}"/>
                        </Decorator>
                    </Border>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

    <Style x:Key="ProgressButtonBaseStyle" BasedOn="{StaticResource ToggleButtonBaseStyle}" TargetType="controls:ProgressButton">
        <Setter Property="Background" Value="{DynamicResource RegionBrush}"/>
        <Setter Property="ProgressStyle" Value="{StaticResource ProgressBarFlat4ProgressButton}"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="controls:ProgressButton">
                    <Border x:Name="Chrome" CornerRadius="{Binding Path=(controls:BorderElement.CornerRadius),RelativeSource={RelativeSource TemplatedParent}}" BorderThickness="{TemplateBinding BorderThickness}" BorderBrush="{TemplateBinding BorderBrush}" Background="{TemplateBinding Background}">
                        <controls:SimplePanel>
                            <ProgressBar x:Name="ProgressBar" Height="Auto" Value="{TemplateBinding Progress}" Maximum="100" Visibility="Collapsed" Style="{TemplateBinding ProgressStyle}"/>
                            <ContentPresenter Name="UnCheckedElement"  Margin="{TemplateBinding Padding}" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}" RecognizesAccessKey="True" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                            <ContentPresenter Name="CheckedElement" Margin="{TemplateBinding Padding}" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}" RecognizesAccessKey="True" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" Visibility="Collapsed" Content="{Binding Path=(controls:StatusSwitchElement.CheckedElement),RelativeSource={RelativeSource TemplatedParent}}"/>
                        </controls:SimplePanel>
                    </Border>
                    <ControlTemplate.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="IsChecked" Value="True">
                            <Setter Property="Visibility" Value="Visible" TargetName="ProgressBar"/>
                            <Setter Property="Visibility" Value="Visible" TargetName="CheckedElement"/>
                        </Trigger>
                        <MultiTrigger>
                            <MultiTrigger.Conditions>
                                <Condition Property="controls:StatusSwitchElement.HideUncheckedElement" Value="True"/>
                                <Condition Property="IsChecked" Value="True"/>
                            </MultiTrigger.Conditions>
                            <Setter Property="Visibility" Value="Collapsed" TargetName="UnCheckedElement"/>
                        </MultiTrigger>
                        <Trigger Property="IsEnabled" Value="False">
                            <Setter Property="Opacity" Value="0.4"/>
                        </Trigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

</ResourceDictionary>