You can achieve this requirement using the following approach:
sender, GridItemEventArgs e)
GridDataItem item = e.Item
item.CssClass = item.ItemIndex % 3 == 0 ?
Hope this helps. Please give it a try and let me know if it works for you.
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Feedback Portal
and vote to affect the priority of the items