title: ComboBoxItem doesn't display
body: <p>I have a style for ComboBox in the Popup. Here is the 
  <a href="https://i.stack.imgur.com/rEemR.png" rel="nofollow noreferrer">Image</a> of my ComboBoxItem 
   <strong>Here is a code:</strong></p>
  
  <pre><code>&lt;Style x:Key="ComboBoxStyle" TargetType="{x:Type ComboBox}"&gt;
          &lt;Setter Property="IsSelected" Value="{DynamicResource ComboBoxItemStyle}"/&gt;
          &lt;Setter Property="Template"&gt;
              &lt;Setter.Value&gt;
                  &lt;ControlTemplate TargetType="{x:Type ComboBox}"&gt;
                      &lt;Grid&gt;
                          &lt;ToggleButton Height="{TemplateBinding Height}"
                                        Style="{StaticResource ToggleButtonStyle}"  
                                        HorizontalAlignment="Right"
                                        Width ="549"
                                        IsChecked="{Binding Path=IsDropDownOpen,Mode=TwoWay,RelativeSource={RelativeSource TemplatedParent}}"
                                        ClickMode="Press"/&gt;
                          &lt;Popup Name="Popup"
                                 IsOpen="{TemplateBinding IsDropDownOpen}"
                                 AllowsTransparency="True" 
                                 Focusable="False"
                                 PopupAnimation="Fade" 
                                 VerticalOffset="10"&gt;
                              &lt;Grid Name="DropDown"
                                    SnapsToDevicePixels="True"
                                    MinWidth="{TemplateBinding ActualWidth}"
                                    MaxHeight="{TemplateBinding MaxDropDownHeight}"&gt;
                                  &lt;Border x:Name="DropDownBorder" CornerRadius="18"/&gt;
                                  &lt;ScrollViewer SnapsToDevicePixels="True" VerticalScrollBarVisibility="Hidden"&gt;
                                      &lt;StackPanel IsItemsHost="True" KeyboardNavigation.DirectionalNavigation="Contained" /&gt;
                                  &lt;/ScrollViewer&gt;
                              &lt;/Grid&gt;
                          &lt;/Popup&gt;
                      &lt;/Grid&gt;
                      &lt;ControlTemplate.Triggers&gt;
                          &lt;Trigger Property="IsGrouping"  Value="true"&gt;
                              &lt;Setter Property="ScrollViewer.CanContentScroll" Value="false"/&gt;
                          &lt;/Trigger&gt;
                          &lt;Trigger SourceName="Popup" Property="Popup.AllowsTransparency" Value="true"&gt;
                              &lt;Setter TargetName="DropDownBorder" Property="Background" Value="White"/&gt;
                          &lt;/Trigger&gt;
                      &lt;/ControlTemplate.Triggers&gt;
                  &lt;/ControlTemplate&gt;
              &lt;/Setter.Value&gt;
          &lt;/Setter&gt;
      &lt;/Style&gt;
  </code></pre>
  
  <p><strong>Styles for ToggleButton and ComboBoxItems:</strong></p>
  
  <pre><code>&lt;Style x:Key="ToggleButtonStyle" TargetType="{x:Type ToggleButton}"&gt;
          &lt;Setter Property="Template"&gt;
              &lt;Setter.Value&gt;
                  &lt;ControlTemplate TargetType="{x:Type ToggleButton}"&gt;
                      &lt;Grid&gt;
                          &lt;Grid.ColumnDefinitions&gt;
                              &lt;ColumnDefinition/&gt;
                              &lt;ColumnDefinition Width="520"/&gt;
                          &lt;/Grid.ColumnDefinitions&gt;
                          &lt;Border x:Name="Border" Grid.ColumnSpan="2" CornerRadius="10,10,10,10" Background="White" /&gt;
                          &lt;Path Data="M12,2A10,10 0 0,1 22,12A10,10 0 0,1 12,22A10,10 0 0,1 2,12A10,10 0 0,1 12,2M7,10L12,15L17,10H7Z" 
                                Fill="#FF16CD1C" HorizontalAlignment="Right" VerticalAlignment="Center" Grid.Column="1" Margin="0,0,10,0"/&gt;
                      &lt;/Grid&gt;
                      &lt;ControlTemplate.Triggers&gt;
                          &lt;Trigger Property="ToggleButton.IsMouseOver" Value="true"&gt;
                              &lt;Setter TargetName="Border" Property="Background" Value="#E1E1E1" /&gt;
                          &lt;/Trigger&gt;
                      &lt;/ControlTemplate.Triggers&gt;
                  &lt;/ControlTemplate&gt;
              &lt;/Setter.Value&gt;
          &lt;/Setter&gt;
      &lt;/Style&gt;
  
  
   &lt;Style x:Key="ComboBoxItemStyle" TargetType="{x:Type ComboBoxItem}"&gt;
          &lt;Setter Property="Background" Value="White"/&gt;
          &lt;Setter Property="IsSelected" Value="{Binding Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}, Path=IsInDesignMode}"/&gt;
          &lt;Setter Property="Template"&gt;
              &lt;Setter.Value&gt;
                  &lt;ControlTemplate TargetType="{x:Type ComboBoxItem}"&gt;
                      &lt;Border Background="{TemplateBinding Background}"
                              CornerRadius="18"
                              BorderThickness="{TemplateBinding BorderThickness}"&gt;
                          &lt;ContentPresenter HorizontalAlignment="Center"/&gt;
                          &lt;Border.Triggers&gt;
                              &lt;EventTrigger RoutedEvent="MouseEnter"&gt;
                                  &lt;BeginStoryboard&gt;
                                      &lt;Storyboard&gt;
                                          &lt;ColorAnimation Storyboard.TargetProperty="(ComboBoxItem.Background).(SolidColorBrush.Color)"
                                          FillBehavior="HoldEnd"
                                          To="#E1E1E1"
                                          Duration="0:0:0.4"/&gt;
                                      &lt;/Storyboard&gt;
                                  &lt;/BeginStoryboard&gt;
                              &lt;/EventTrigger&gt;
                              &lt;EventTrigger RoutedEvent="MouseLeave"&gt;
                                  &lt;BeginStoryboard&gt;
                                      &lt;Storyboard&gt;
                                          &lt;ColorAnimation Storyboard.TargetProperty="(ComboBoxItem.Background).(SolidColorBrush.Color)"
                                                          FillBehavior="HoldEnd"
                                                          To="#FFFFFF"
                                                          Duration="0:0:0.4"/&gt;
                                      &lt;/Storyboard&gt;
                                  &lt;/BeginStoryboard&gt;
                              &lt;/EventTrigger&gt;
                          &lt;/Border.Triggers&gt;
                      &lt;/Border&gt;
                  &lt;/ControlTemplate&gt;
              &lt;/Setter.Value&gt;
          &lt;/Setter&gt;
      &lt;/Style&gt;
  </code></pre>
  
  <p>When I choose any item from the List, it doesn't display.Just a white space. I tried to Bind SelectionBoxItem, but it doesn't work.
   I will be so happy if I get answer.
   Thanks.</p>