How to make a line fill symbol

Public Sub LineFillSymbol()
    ' Set the color for the line symbol in the fill.
    Dim rgbColorCls As ESRI.ArcGIS.Display.IRgbColor = New ESRI.ArcGIS.Display.RgbColorClass
    With rgbColorCls
        .Red = 138
        .Green = 151
        .Blue = 255
    End With
    
    ' Create the line symbol to be used.
    Dim cartographicLineSymbolCls As ESRI.ArcGIS.Display.ICartographicLineSymbol = New ESRI.ArcGIS.Display.CartographicLineSymbolClass
    With cartographicLineSymbolCls
        .Cap = ESRI.ArcGIS.Display.esriLineCapStyle.esriLCSButt
        .Join = ESRI.ArcGIS.Display.esriLineJoinStyle.esriLJSMitre
        .Color = rgbColorCls
        .Width = 2
    End With
    
    ' Create the line fill symbol.
    Dim lineFillSymbolCls As ESRI.ArcGIS.Display.ILineFillSymbol = New ESRI.ArcGIS.Display.LineFillSymbolClass
    With lineFillSymbolCls
        .Angle = 45
        .Separation = 10
        .Offset = 5
    End With
    
    lineFillSymbolCls.LineSymbol = cartographicLineSymbolCls
    
End Sub

public void LineFillSymbol()
{
    // Set the color for the line symbol in the fill.
    ESRI.ArcGIS.Display.IRgbColor rgbColorCls = new
        ESRI.ArcGIS.Display.RgbColorClass();
    rgbColorCls.Red = 138;
    rgbColorCls.Green = 151;
    rgbColorCls.Blue = 255;

    // Create the line symbol to be used.
    ESRI.ArcGIS.Display.ICartographicLineSymbol cartographicLineSymbolCls = new
        ESRI.ArcGIS.Display.CartographicLineSymbolClass();
    cartographicLineSymbolCls.Cap = ESRI.ArcGIS.Display.esriLineCapStyle.esriLCSButt;
    cartographicLineSymbolCls.Join =
        ESRI.ArcGIS.Display.esriLineJoinStyle.esriLJSMitre;
    cartographicLineSymbolCls.Color = rgbColorCls;
    cartographicLineSymbolCls.Width = 2;

    // Create the line fill symbol.
    ESRI.ArcGIS.Display.ILineFillSymbol lineFillSymbolCls = new
        ESRI.ArcGIS.Display.LineFillSymbolClass();
    lineFillSymbolCls.Angle = 45;
    lineFillSymbolCls.Separation = 10;
    lineFillSymbolCls.Offset = 5;
    lineFillSymbolCls.LineSymbol = cartographicLineSymbolCls;
}