Style_and_groubox

 <Style TargetType="ListBoxItem" BasedOn="{StaticResource {x:Type ListBoxItem}}" x:Key="ExtraStyle">
            <Setter Property="Opacity" Value="0.2"/>
            <Style.Triggers>
                <MultiTrigger>
                    <MultiTrigger.Conditions>
                        <Condition Property="IsSelected" Value="False"/>
                        <Condition Property="IsMouseOver" Value="True"/>
                    </MultiTrigger.Conditions>
                    <MultiTrigger.EnterActions>
                        <BeginStoryboard>
                            <Storyboard>
                                <DoubleAnimation Duration="0:0:0.5" Storyboard.TargetProperty="Opacity" To="1.0"/>
                            </Storyboard>
                        </BeginStoryboard>
                    </MultiTrigger.EnterActions>
                    <MultiTrigger.ExitActions>
                        <BeginStoryboard>
                            <Storyboard>
                                <DoubleAnimation Duration="0:0:0.5" Storyboard.TargetProperty="Opacity" />
                            </Storyboard>
                        </BeginStoryboard>
                    </MultiTrigger.ExitActions>
                </MultiTrigger>
                <Trigger Property="IsSelected" Value="True">
                    <Trigger.Setters>
                        <Setter Property="Opacity" Value="1.0"/>
                    </Trigger.Setters>
                </Trigger>


            </Style.Triggers>
        </Style>

<GroupBox Header="Suchergebnis" Grid.Row="1" Margin="5,5,5,5">
                <ListBox Margin="5,5,5,5" ItemsSource="{Binding GetListable}" SelectedItem="{Binding PersData}"  ItemContainerStyle="{StaticResource ExtraStyle}" >
                    <ListBox.ItemTemplate>
                        <DataTemplate>
                            <StackPanel>
                                <Grid>
                                    <Grid.ColumnDefinitions>
                                        <ColumnDefinition Width="165"/>
                                        <ColumnDefinition Width="100"/>
                                    </Grid.ColumnDefinitions>
                                    <ListBoxItem Grid.Column="0" Content="{Binding Fullname, Mode=OneWay}" FontWeight="Bold" FontSize="14"/>
                                    <ListBoxItem Grid.Column="1" Content="{Binding Geburtsdatum}" Margin="0,0,0,0" FontSize="14"/>
                                </Grid>
                            </StackPanel>
                        </DataTemplate>
                    </ListBox.ItemTemplate>
                </ListBox>
            </GroupBox>