A way to correct the borderThickess of GroupBox when the value of basecolors is dark

[verk123]

from:https://docs.microsoft.com/en-us/dotnet/framework/wpf/controls/how-to-define-a-groupbox-template
Before：

After：

Add the following code into RibbonGroupBox.xaml

<BorderGapMaskConverter x:Key="BorderGapMaskConverter"/> <Style x:Key="{x:Type GroupBox}" TargetType="{x:Type GroupBox}"> <!--<Setter Property="BorderBrush" Value="Gray"/> <Setter Property="Foreground" Value="White"/>--> <Setter Property="BorderThickness" Value="1"/> <Setter Property="Template"> <Setter.Value> <ControlTemplate TargetType="{x:Type GroupBox}"> <Grid> <Grid.ColumnDefinitions> <ColumnDefinition Width="4"/> <ColumnDefinition Width="Auto"/> <ColumnDefinition Width="*"/> <ColumnDefinition Width="4"/> </Grid.ColumnDefinitions> <Grid.RowDefinitions> <RowDefinition Height="Auto"/> <RowDefinition Height="Auto"/> <RowDefinition Height="*"/> <RowDefinition Height="4"/> </Grid.RowDefinitions> <Border CornerRadius="4" Grid.Row="1" Grid.RowSpan="3" Grid.Column="0" Grid.ColumnSpan="4" BorderThickness="{TemplateBinding BorderThickness}" BorderBrush="Transparent" Background="{TemplateBinding Background}"/> <!-- ContentPresenter for the header --> <Border x:Name="Header" Padding="6,0,6,0" Grid.Row="0" Grid.RowSpan="2" Grid.Column="1"> <ContentPresenter ContentSource="Header" RecognizesAccessKey="True" /> </Border> <!-- Primary content for GroupBox --> <ContentPresenter Grid.Row="2" Grid.Column="1" Grid.ColumnSpan="2" Margin="{TemplateBinding Padding}"/> <Border CornerRadius="0" Grid.Row="1" Grid.RowSpan="3" Grid.ColumnSpan="4" BorderThickness="{TemplateBinding BorderThickness}" BorderBrush="{TemplateBinding BorderBrush}"> <Border.OpacityMask> <MultiBinding Converter= "{StaticResource BorderGapMaskConverter}" ConverterParameter="6"> <Binding ElementName="Header" Path="ActualWidth"/> <Binding RelativeSource="{RelativeSource Self}" Path="ActualWidth"/> <Binding RelativeSource="{RelativeSource Self}" Path="ActualHeight"/> </MultiBinding> </Border.OpacityMask> </Border> </Grid> </ControlTemplate> </Setter.Value> </Setter> </Style>

[batzen]

Thanks for your suggestion.
I might add this, or something like this, to the showcase application to improve it's look.

But styling default WPF elements, outside of the ribbon itself, is not the scope of Fluent.Ribbon.