Issue with DatagridHeaderText style of wpf datagrid

Hi,

I am using the wpf datagrid, there are columns which are dynamically generated.I set the fontsize as :72", the data which is displayed on the grid has fonstsize 72 but, the headertext "Interest Rates" fontsize is not changing.

<Style x:Key="HeaderTemplate" TargetType="{x:Type DataGridColumnHeader}">
                <Setter Property="SeparatorBrush" Value="#FFD6D9E0" />
                <!--  <Setter Property="Padding" Value="6,0,6,0" />  -->
                <!--  <Setter Property="Height" Value="24" />  -->
                <Setter Property="FontSize" Value="72" />
            </Style>

need your help for fixing this issue.please also find attached the screenshot.This is the default style, I need to add the fontsize dynamically from code, but the issue is the default style is also not getting updated.

Regards

chaituatp