public static IList<SymbolStyleItem> SearchSymbols( 
   StyleProjectItem styleProjectItem,
   StyleItemType type,
   string searchString
)

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

//Build geometry
List<Coordinate2D> plCoords = new List<Coordinate2D>();
plCoords.Add(new Coordinate2D(1, 8.5));
plCoords.Add(new Coordinate2D(1.66, 9));
plCoords.Add(new Coordinate2D(2.33, 8.1));
plCoords.Add(new Coordinate2D(3, 8.5));
Polyline linePl = PolylineBuilderEx.CreatePolyline(plCoords);

//Reference a line symbol in a style
var ProjectStyles = Project.Current.GetItems<StyleProjectItem>();
StyleProjectItem style = ProjectStyles.First(x => x.Name == "ArcGIS 2D");
var symStyle = style.SearchSymbols(StyleItemType.LineSymbol, "Line with 2 Markers")[0];
CIMLineSymbol lineSym = symStyle.Symbol as CIMLineSymbol;
lineSym.SetSize(20);

//Set symbolology, create and add element to layout
//CIMLineSymbol lineSym = SymbolFactory.Instance.ConstructLineSymbol(ColorFactory.Instance.BlueRGB, 4.0, SimpleLineStyle.Solid);
ElementFactory.Instance.CreateGraphicElement(
  container, linePl, lineSym, "New Line");

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

//Build geometry
Coordinate2D coord2D = new Coordinate2D(2.0, 10.0);

//Reference a point symbol in a style
StyleProjectItem stylePrjItm = Project.Current.GetItems<StyleProjectItem>()
         .FirstOrDefault(item => item.Name == "ArcGIS 2D");
SymbolStyleItem symStyleItm = stylePrjItm.SearchSymbols(
                      StyleItemType.PointSymbol, "City Hall")[0];
CIMPointSymbol pointSym = symStyleItm.Symbol as CIMPointSymbol;
pointSym.SetSize(50);

var elemInfo = new ElementInfo()
{
  CustomProperties = new List<CIMStringMap>() {
     new CIMStringMap() { Key = "Key1", Value = "Value1"},
     new CIMStringMap() { Key = "Key2", Value = "Value2"}
   },
  Anchor = Anchor.TopRightCorner,
  Rotation = 45.0
};

var graphic = GraphicFactory.Instance.CreateSimpleGraphic(
                              coord2D.ToMapPoint(), pointSym);

ElementFactory.Instance.CreateGraphicElement(
  container, graphic, "New Point", true, elemInfo);

//Create a simple 2D point graphic and apply an existing point style item as the symbology.

//Construct on the worker thread
await QueuedTask.Run(() =>
{
  //Build 2D point geometry  
  Coordinate2D coord2D = new Coordinate2D(2.0, 10.0);

  //(optionally) Reference a point symbol in a style
  StyleProjectItem ptStylePrjItm = Project.Current.GetItems<StyleProjectItem>()
                                .FirstOrDefault(item => item.Name == "ArcGIS 2D");
  SymbolStyleItem ptSymStyleItm = ptStylePrjItm.SearchSymbols(
                                         StyleItemType.PointSymbol, "City Hall")[0];
  CIMPointSymbol pointSym = ptSymStyleItm.Symbol as CIMPointSymbol;
  pointSym.SetSize(50);

  //Set symbolology, create and add element to layout

  //An alternative simple symbol is also commented out below.
  //This would elminate the four optional lines of code above that
  //reference a style.

  //CIMPointSymbol pointSym = SymbolFactory.Instance.ConstructPointSymbol(
  //                  ColorFactory.Instance.RedRGB, 25.0, SimpleMarkerStyle.Star);  
  //At 2.x - GraphicElement ptElm =
  //                    LayoutElementFactory.Instance.CreatePointGraphicElement(
  //                                        layout, coord2D, pointSym);

  GraphicElement ptElm = ElementFactory.Instance.CreateGraphicElement(
                                 container, coord2D.ToMapPoint(), pointSym);
  ptElm.SetName("New Point");
});

//Create a simple 2D line graphic and apply an existing line
//style item as the symbology.

//Construct on the worker thread
await QueuedTask.Run(() =>
{
  //Build 2d line geometry
  List<Coordinate2D> plCoords = new List<Coordinate2D>();
  plCoords.Add(new Coordinate2D(1, 8.5));
  plCoords.Add(new Coordinate2D(1.66, 9));
  plCoords.Add(new Coordinate2D(2.33, 8.1));
  plCoords.Add(new Coordinate2D(3, 8.5));
  //At 2.x - Polyline linePl = PolylineBuilder.CreatePolyline(plCoords);
  Polyline linePl = PolylineBuilderEx.CreatePolyline(plCoords);

  //(optionally) Reference a line symbol in a style
  StyleProjectItem lnStylePrjItm = Project.Current.GetItems<StyleProjectItem>()
                                .FirstOrDefault(item => item.Name == "ArcGIS 2D");
  SymbolStyleItem lnSymStyleItm = lnStylePrjItm.SearchSymbols(
                                StyleItemType.LineSymbol, "Line with 2 Markers")[0];
  CIMLineSymbol lineSym = lnSymStyleItm.Symbol as CIMLineSymbol;
  lineSym.SetSize(20);

  //Set symbolology, create and add element to layout

  //An alternative simple symbol is also commented out below.
  //This would elminate the four optional lines of code above that
  //reference a style.
  //
  //CIMLineSymbol lineSym = SymbolFactory.Instance.ConstructLineSymbol(
  //         ColorFactory.Instance.BlueRGB, 4.0, SimpleLineStyle.Solid);  
  //At 2.x - GraphicElement lineElm =
  //        LayoutElementFactory.Instance.CreateLineGraphicElement(
  //                                            layout, linePl, lineSym);

  GraphicElement lineElm = ElementFactory.Instance.CreateGraphicElement(
                                              container, linePl, lineSym);
  lineElm.SetName("New Line");
});

public Task<IList<SymbolStyleItem>> GetPointSymbolsFromStyleAsync(StyleProjectItem style, string searchString)
{
  if (style == null)
    throw new System.ArgumentNullException();

  //Search for point symbols
  return QueuedTask.Run(() => style.SearchSymbols(StyleItemType.PointSymbol, searchString));
}

public Task<IList<SymbolStyleItem>> GetLineSymbolsFromStyleAsync(StyleProjectItem style, string searchString)
{
  if (style == null)
    throw new System.ArgumentNullException();

  //Search for line symbols
  return QueuedTask.Run(() => style.SearchSymbols(StyleItemType.LineSymbol, searchString));
}

public async Task<IList<SymbolStyleItem>> GetPolygonSymbolsFromStyleAsync(StyleProjectItem style, string searchString)
{
  if (style == null)
    throw new System.ArgumentNullException();

  //Search for polygon symbols
  return await QueuedTask.Run(() => style.SearchSymbols(StyleItemType.PolygonSymbol, searchString));
}

  // var map = MapView.Active.Map;
  // if (map == null)
  //        return;
  // var pointFeatureLayer =
  //       map.GetLayersAsFlattenedList()
  //          .OfType<FeatureLayer>()
  //         .Where(fl => fl.ShapeType == esriGeometryType.esriGeometryPoint);
  //   await ApplySymbolToFeatureLayerAsync(pointFeatureLayer.FirstOrDefault(), "Fire Station");

  public Task ApplySymbolToFeatureLayerAsync(FeatureLayer featureLayer, string symbolName)
  {
    return QueuedTask.Run(async () =>
    {
      //Get the ArcGIS 2D System style from the Project
      var arcGIS2DStyle =
Project.Current.GetItems<StyleProjectItem>().FirstOrDefault(s => s.Name == "ArcGIS 2D");

      //Search for the symbolName style items within the ArcGIS 2D style project item.
      var items = await QueuedTask.Run(() =>
      arcGIS2DStyle.SearchSymbols(StyleItemType.PointSymbol, symbolName));

      //Gets the CIMSymbol
      CIMSymbol symbol = items.FirstOrDefault().Symbol;

      //Get the renderer of the point feature layer
      CIMSimpleRenderer renderer = featureLayer.GetRenderer() as CIMSimpleRenderer;

      //Set symbol's real world setting to be the same as that of the feature layer
      symbol.SetRealWorldUnits(featureLayer.UsesRealWorldSymbolSizes);

      //Apply the symbol to the feature layer's current renderer
      renderer.Symbol = symbol.MakeSymbolReference();

      //Appy the renderer to the feature layer
      featureLayer.SetRenderer(renderer);
    });
  }