<Button VerticalAlignment="Center" HorizontalAlignment="Center">
  <Button.Background>	
    <LinearGradientBrush StartPoint="0,0" EndPoint="0,1">
      <LinearGradientBrush.GradientStops>
        <GradientStop Offset="0"    Color="#800" />
        <GradientStop Offset="0.35" Color="Red" />
        <GradientStop Offset="1"    Color="#500" />
      </LinearGradientBrush.GradientStops>
    </LinearGradientBrush>
  </Button.Background>
  Click me
</Button>

