public class CIMBalloonCallout : CIMCallout, System.ComponentModel.INotifyPropertyChanged, System.Xml.Serialization.IXmlSerializable  

/// <summary>
/// Creates a black banner balloon callout text symbol. The [CIMBalloonCallout](https://pro.arcgis.com/en/pro-app/sdk/api-reference/#topic487.html) created is a rectangular polygon with rounded corners.
/// ![lineCallOut](https://ArcGIS.github.io/arcgis-pro-sdk/images/Labeling/banner-callout.png)
/// </summary>
{
  //create a text symbol
  //Note: Run this code inside a QueuedTask
  var textSymbolBalloonCallout = SymbolFactory.Instance.ConstructTextSymbol(ColorFactory.Instance.WhiteRGB, 11, "Corbel", "Regular");
  //A balloon callout
  var balloonCallout = new CIMBalloonCallout();
  //set the callout's style
  balloonCallout.BalloonStyle = BalloonCalloutStyle.RoundedRectangle;
  //Create a solid fill polygon symbol for the callout.
  var polySymbol = SymbolFactory.Instance.ConstructPolygonSymbol(ColorFactory.Instance.BlackRGB, SimpleFillStyle.Solid);
  //Set the callout's background to be the black polygon symbol
  balloonCallout.BackgroundSymbol = polySymbol;
  //margin inside the callout to place the text
  balloonCallout.Margin = new CIMTextMargin
  {
    Left = 5,
    Right = 5,
    Bottom = 5,
    Top = 5
  };
  //assign the callout to the text symbol's callout property
  textSymbolBalloonCallout.Callout = balloonCallout;
  //Refer to the snippet "How to apply a Text Symbol to labels of a layer" below to see how to apply this text symbol to a label class
}