The stylesheet distributed by the Button.Flom.css applies to RadButton.
The FontIconButton, ImageButton, LinkButton and PushButton button types provided by the GridButtonColumn column of RadGrid are not based on RadButton and for this reason they are not styled by the classes defined in the Button.Flom.css file.
What you can do is to set your own CSS class CustomButtonClass in the Button.Flom.css and to set it as a value of the btnFSR.ButtonCssClass property
GridButtonColumn btnFSR =
This way you will be able to style the GridButtonColumn column buttons as per your criteria.
Another approach is to add a GridTemplateColumn
column (instead of a GridButtonColumn column) and set in it RadButton buttons that will be styled by the classes defined in the Button.Flom.css file.