effector.plugin.lib/Effector.Plugin.Lib/Themes/Generic.xaml

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:sys="clr-namespace:System;assembly=mscorlib"
                    xmlns:local="clr-namespace:Effector.Plugin.Lib">

   <local:CaptionHeightConverter x:Key="CaptionHeightConverter"/>
   
   <Style TargetType="{x:Type local:EgtWindow}" BasedOn="{StaticResource {x:Type Window}}">
      <Setter Property="WindowChrome.WindowChrome">
         <Setter.Value>
            <WindowChrome CaptionHeight="{Binding TitleBarHeight, RelativeSource={RelativeSource AncestorType={x:Type local:EgtWindow}}}" 
                          GlassFrameThickness="0"
                          CornerRadius="0"
                          ResizeBorderThickness="{x:Static SystemParameters.WindowResizeBorderThickness}"/>
         </Setter.Value>
      </Setter>
      <Setter Property="Template">
         <Setter.Value>
            <ControlTemplate TargetType="{x:Type Window}">
               <Border BorderThickness="0"
                       BorderBrush="LightGray"
                       Background="{TemplateBinding Background}">
                  <ContentPresenter Grid.Row="1" 
                                    Content="{TemplateBinding Content}"/>
               </Border>
            </ControlTemplate>
         </Setter.Value>
      </Setter>
      <Style.Triggers>
         <Trigger Property="WindowState" Value="Maximized">
            <Setter Property="WindowChrome.WindowChrome">
               <Setter.Value>
                  <WindowChrome CaptionHeight="{Binding TitleBarHeight, RelativeSource={RelativeSource AncestorType={x:Type local:EgtWindow}}, Converter={StaticResource CaptionHeightConverter}}" 
                          GlassFrameThickness="0"
                          CornerRadius="0"
                          ResizeBorderThickness="{x:Static SystemParameters.WindowResizeBorderThickness}"/>
               </Setter.Value>
            </Setter>
            <Setter Property="Template">
               <Setter.Value>
                  <ControlTemplate TargetType="{x:Type Window}">
                     <!--bordo necessario per evitare la parte che esce dallo schermo-->
                     <Border BorderThickness="7"
                             BorderBrush="LightGray"
                             Background="{TemplateBinding Background}">
                        <ContentPresenter Grid.Row="1"
                                          Content="{TemplateBinding Content}"/>
                     </Border>
                  </ControlTemplate>
               </Setter.Value>
            </Setter>
         </Trigger>
      </Style.Triggers>
   </Style>

</ResourceDictionary>