<Style TargetType="{x:Type DataGridColumnHeader}" x:Key="DataGridColumnHeader">
            <Setter Property="Foreground" Value="White" />
            <Setter Property="Background" Value="Gray" />
            <Setter Property="Height" Value="23" />  
            <Setter Property="HorizontalContentAlignment" Value="Center"/>
            <Style.Triggers>
                <Trigger Property="IsMouseOver" Value="True">
                    <Setter Property="Background" Value="Blue" />
                </Trigger>
            </Style.Triggers>
        </Style>