<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

    <Style TargetType="GroupBox">
        <Setter Property="FontSize" Value="20" />
        <Setter Property="BorderBrush" Value="Black" />
    </Style>
</ResourceDictionary>