WPF Highlight brush for Combobox template - wpf

Question

I can't figure out how to set the Highlight brush of a Combobox (the color that will mark the item being selected on mouse over) to a certain Brush. I have used Edit Template -> Copy to get copy of the template where I try to set the SystemColors.HighlightBrushKey. I have seen answers that one should be able to set the brush by defining it like this in the Style resource, but it just does not work.
I have also tried to set the Grid's Style.Resource in which the comobox is placed, that did not help either.
Please see line 3 and line 15 where I set the color to red. No effect. What am I doing wrong?
<Style x:Key="TeachpendantVMVisionServerComboBoxStyle" TargetType="{x:Type ComboBox}">
<Style.Resources>
<SolidColorBrush x:Key="{x:Static SystemColors.HighlightBrushKey}" Color="Red" />
<SolidColorBrush x:Key="{x:Static SystemColors.ControlBrushKey}" Color="Red" />
</Style.Resources>
<Setter Property="HorizontalContentAlignment" Value="Center"/>
<Setter Property="VerticalContentAlignment" Value="Center"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ComboBox}">
<Grid x:Name="grid">
<Grid.Style>
<Style>
<Style.Resources>
<SolidColorBrush x:Key="{x:Static SystemColors.HighlightBrushKey}" Color="Red" />
<SolidColorBrush x:Key="{x:Static SystemColors.ControlBrushKey}" Color="Red" />
</Style.Resources>
</Style>
</Grid.Style>
<Grid.ColumnDefinitions>
<ColumnDefinition/>
<ColumnDefinition MaxWidth="18"/>
</Grid.ColumnDefinitions>
<VisualStateManager.VisualStateGroups>
<VisualStateGroup x:Name="ValidationStates">
<VisualState x:Name="Valid"/>
<VisualState x:Name="InvalidFocused">
<Storyboard>
<ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="(Border.BorderBrush)" Storyboard.TargetName="PART_EditableTextBox">
<DiscreteObjectKeyFrame KeyTime="0">
<DiscreteObjectKeyFrame.Value>
<SolidColorBrush Color="Red"/>
</DiscreteObjectKeyFrame.Value>
</DiscreteObjectKeyFrame>
</ObjectAnimationUsingKeyFrames>
<ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="(Shape.Fill)" Storyboard.TargetName="path">
<DiscreteObjectKeyFrame KeyTime="0" Value="{StaticResource MoveTextBox.Invalid.BorderBrush}"/>
</ObjectAnimationUsingKeyFrames>
<ColorAnimationUsingKeyFrames Storyboard.TargetProperty="(Border.BorderBrush).(SolidColorBrush.Color)" Storyboard.TargetName="toggleButton">
<EasingColorKeyFrame KeyTime="0" Value="#FFFB0000"/>
</ColorAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
<VisualState x:Name="InvalidUnfocused">
<Storyboard>
<ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="(Border.BorderBrush)" Storyboard.TargetName="PART_EditableTextBox">
<DiscreteObjectKeyFrame KeyTime="0" Value="{StaticResource MoveTextBox.Invalid.BorderBrush}"/>
</ObjectAnimationUsingKeyFrames>
<ColorAnimationUsingKeyFrames Storyboard.TargetProperty="(Border.BorderBrush).(SolidColorBrush.Color)" Storyboard.TargetName="toggleButton">
<EasingColorKeyFrame KeyTime="0" Value="Red"/>
</ColorAnimationUsingKeyFrames>
<ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="(Shape.Fill)" Storyboard.TargetName="path">
<DiscreteObjectKeyFrame KeyTime="0">
<DiscreteObjectKeyFrame.Value>
<SolidColorBrush Color="Red"/>
</DiscreteObjectKeyFrame.Value>
</DiscreteObjectKeyFrame>
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
</VisualStateGroup>
</VisualStateManager.VisualStateGroups>
<TextBox x:Name="PART_EditableTextBox"
Padding="5,0,0,0"
Height="{TemplateBinding Height}">
<TextBox.Template>
<ControlTemplate TargetType="{x:Type TextBox}">
<Grid>
<Border
x:Name="border"
CornerRadius="3,0,0,3"
BorderThickness="1,1,0,1"
Background="{DynamicResource Button.Static.Background}"
BorderBrush="{DynamicResource Button.Static.Background}">
<ScrollViewer x:Name="PART_ContentHost"/>
</Border>
</Grid>
</ControlTemplate>
</TextBox.Template>
</TextBox>
<ToggleButton x:Name="toggleButton" Grid.Column="1" Margin="0"
Height="{TemplateBinding Height}"
Focusable="False"
IsChecked="{Binding IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}"
ClickMode="Press" BorderBrush="#FFABADB3">
<ToggleButton.Template>
<ControlTemplate TargetType="{x:Type ToggleButton}">
<Border
Background="{DynamicResource Button.Checked.Background}"
x:Name="border"
CornerRadius="0,3,3,0"
BorderThickness="0,1,1,1"
BorderBrush="{DynamicResource Button.Static.Background}">
<ContentPresenter />
</Border>
</ControlTemplate>
</ToggleButton.Template>
<Path x:Name="path" Grid.Column="1"
HorizontalAlignment="Center"
VerticalAlignment="Center"
Data="M 0 0 L 4 4 L 8 0 Z"
Fill="Gold" />
</ToggleButton>
<ContentPresenter x:Name="ContentSite"
Content="{TemplateBinding SelectionBoxItem}"
ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}"
ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}"
VerticalAlignment="Center"
HorizontalAlignment="Right"
Margin="5,0,0,0" RecognizesAccessKey="True"/>
<Popup x:Name="Popup"
Placement="Bottom"
IsOpen="{TemplateBinding IsDropDownOpen}"
AllowsTransparency="True"
Focusable="True"
PopupAnimation="Slide"
OverridesDefaultStyle="True">
<Grid x:Name="DropDown"
SnapsToDevicePixels="True"
MinWidth="{TemplateBinding ActualWidth}"
MaxHeight="{TemplateBinding MaxDropDownHeight}">
<Border
x:Name="DropDownBorder"
BorderThickness="1"
CornerRadius="5"
Background="Azure"
BorderBrush="DarkGray">
</Border>
<ScrollViewer Margin="4,6,4,6" SnapsToDevicePixels="True">
<StackPanel IsItemsHost="True" KeyboardNavigation.DirectionalNavigation="Contained" />
</ScrollViewer>
</Grid>
</Popup>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
<Setter Property="Validation.ErrorTemplate">
<Setter.Value>
<ControlTemplate/>
</Setter.Value>
</Setter>
</Style>

Answer 1

It was fairly simple after all (but not obvious where to find it).
Just edit a copy of the ItemsContainerStyle and all these Brushes can be set from there.
To Change the layout of the ComboBox (creating a round combobox or changing colors)
Style="{DynamicResource MyComboBoxStyle}"
To Change the hoover and selected Highlight colors
ItemContainerStyle="{DynamicResource MyComboBoxItemS}"
The complete Combobox would look like this then in XAML
<ComboBox x:Name="positionsComboBox"
Grid.Column="1"
Grid.ColumnSpan="3"
IsReadOnly = "True"
IsEditable = "False"
Margin="3,0,3,0"
ItemsSource="{Binding IDs, Source={StaticResource Locator}, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"
SelectedValue="{Binding SelectedID, Source={StaticResource Locator}, Mode=TwoWay}"
Style="{DynamicResource MyComboBoxStyle}"
IsSynchronizedWithCurrentItem="True"
ItemContainerStyle="{DynamicResource MyComboBoxItemContainerStyle}"
FontWeight="Bold"
FontSize="24"/>