Hello Nikolay,

while

<ig:XamGrid.CellStyle>
                    <Style TargetType="ig:CellControl">
                        <Setter Property="FontSize" Value="14" />
                    </Style>

</ig:XamGrid.CellStyle>

certainly works, apparently I can't databind to that property. If I try:

 <ig:XamGrid.CellStyle>
                    <Style TargetType="ig:CellControl">
                        <Setter Property="FontSize" Value="{Binding Path=XamGridCellFontSize}" />
                    </Style>

 </ig:XamGrid.CellStyle>

it won't work. I find curious that, while any other control would inherit the usercontrol fontsize (with many other properties)
the XamGrid won't. It is a problem for me, since I set the FontSize I want to use according to the user's screen resolution .
Usually I'm done with 1 line of code (I set the Page or UserControl FontSize and every control in it will inherit it.
With the XamGrid I have to hard code the value in Xaml.
Am I doing something wrong? 

Thank you Nikolay.  It worked.