I do not see BeforeEventRenderArgs in the object browser, so can not use sample code in 
https://doc.daypilot.org/calendar/event-customization/
 I have the following using statement "using DayPilot.Web.Mvc.Events.Calendar;"   I encounter the following error when using the below sample code.
"The type or namespace name 'BeforeEventRenderArgs' could not be found (are you missing a using directive or an assembly reference?"
public class Dpc: DayPilotCalendar {
  // ...
  protected override void OnBeforeEventRender(BeforeEventRenderArgs e)
  {
    if ((string)e.DataItem["type"] == "special")  // "type" field must be available in the DataSource
    {
      e.CssClass = "special";
      e.BackgroundColor = "lightyellow";
      e.Html = "<i>WARNING: This is an unusual event.</i><br>" + e.Html;
    }
  }
}
Any help is greatly appreciated.