public CIMColor GreyRGB {get;}

//Must be on QueuedTask.Run(() => { ...

//Build geometry
Coordinate2D center = new Coordinate2D(2, 2.75);
var eabElp = new EllipticArcBuilderEx(center, 0, 1, 0.45, 
                                       ArcOrientation.ArcClockwise);
var ellipse = eabElp.ToSegment();

//Set symbolology, create and add element to layout
CIMStroke outline = SymbolFactory.Instance.ConstructStroke(
                                ColorFactory.Instance.GreenRGB, 2.0,
                        SimpleLineStyle.Dot);
CIMPolygonSymbol ellipseSym = SymbolFactory.Instance.ConstructPolygonSymbol(
                         ColorFactory.Instance.GreyRGB, SimpleFillStyle.Vertical, 
                                                  outline);

var poly = PolygonBuilderEx.CreatePolygon(
  PolylineBuilderEx.CreatePolyline(ellipse, AttributeFlags.AllAttributes));

var elpElm = ElementFactory.Instance.CreateGraphicElement(
  container, poly, ellipseSym, "New Ellipse");