ajuste o botão de saída wpf

<Window 
    x:Class="WafClient.Presentation.Views.SampleWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:u="clr-namespace:WafClient.Presentation.Behaviors"
    ResizeMode="NoResize"
    u:WindowBehavior.HideCloseButton="True">
    ...
</Window>
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