WPF XAML Ressources

<UserControl.Resources>
 <Style x:Key="{x:Type ComboBox}" TargetType="ComboBox">
 <Style TargetType="{x:Type TabControl}" />
 
 <ResourceDictionary>
  <ResourceDictionary.MergedDictionaries>
   <ResourceDictionary Source="/PVStyles;component/PVStyles.xaml" />
   <ResourceDictionary Source="ExpanderResource.xaml" />
  </ResourceDictionary.MergedDictionaries>
  </ResourceDictionary>
</UserControl.Resources>
 
<!-- ExpanderResource.xaml --!>
<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:igDP="http://infragistics.com/DataPresenter"
                    xmlns:igRibbon="http://infragistics.com/Ribbon"
                    xmlns:igEditors="http://infragistics.com/Editors"
                    xmlns:igWindows="http://infragistics.com/Windows"
                    xmlns:igThemes="http://infragistics.com/Themes"
                    xmlns:igDock="http://infragistics.com/DockManager"
                    xmlns:PresentationOptions="http://schemas.microsoft.com/winfx/2006/xaml/presentation/options" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
 
    <LinearGradientBrush x:Key="DarkBrush" StartPoint="0,0" EndPoint="0,1">
        <GradientBrush.GradientStops>
            <GradientStopCollection>
                <GradientStop Color="#FF6DACC8" Offset="0.0"/>
                <GradientStop Color="#FF6DACC8" Offset="1.0"/>
            </GradientStopCollection>
        </GradientBrush.GradientStops>
    </LinearGradientBrush>
 
  <Style TargetType="Expander" />
</ResourceDictionary>