i created a ResourceDictionary , and defined a style for Windows
<Style TargetType="{x:Type Window}" x:Key="WindowDefaultStyle">
<Setter Property="FontFamily" Value="Tahoma" />
<Setter Property="FlowDirection" Value="RightToLeft" />
<Setter Property="FontSize" Value="11" />
</Style>
<!-- Window file -->
<Window Style="{DynamicResource ResourceKey=WindowDefaultStyle}">
apply style in design but when run program not apply.:(
Note: I have updated my code so other people can simply use it.