For example we can define the style in app.xaml page as follows.
<Application.Resources>
<Style x:Key="MyTextBoxStyle" TargetType="TextBox">
<Setter Property="FontFamily" Value="Verdana"/>
<Setter Property="Margin" Value="10,0,10,0"/>
<Setter Property="FontSize" Value="20"/>
<Setter Property="Height" Value="25"/>
<Setter Property="Width" Value="150"/>
<Setter Property="TextWrapping" Value="Wrap"/>
</Style>
</Application.Resources>
The above style targets to TextBox controls. Now , you can set the style to the Style property of the TextBox control in the page level as follows.
<TextBox x:Name="txtName" Style="{StaticResource MyTextBoxStyle}" />