How to use a system color in a lineargradientbrush in wpf

I have a gradient background for my window

<Window.Background>
        <LinearGradientBrush StartPoint="0,0" EndPoint="0,1">
            <GradientStop Offset="0" Color="White" />
            <GradientStop Offset="0" Color="Black" />
        </LinearGradientBrush>
    <开发者_开发知识库;/Window.Background>

I would like to replace the black gradient stop with the system color for control faces (the color buttons and dialog boxes are by default)

Whats the syntax?

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You can specify a Color through the static-extension:

<GradientStop Offset="0" Color="{x:Static SystemColors.ActiveBorderColor}" />