How to customize the combobox button for combobox celltype in WinForms GridGroupingControl?

//Triggering the event.
this.gridGroupingControl1.TableControl.DrawCellButtonBackground += new GridDrawCellButtonBackgroundEventHandler(TableControl_DrawCellButtonBackground);
 
//Event customization. 
 void TableControl_DrawCellButtonBackground(object sender, GridDrawCellButtonBackgroundEventArgs e)
 {
     if (e.Style.CellType == GridCellTypeName.ComboBox)
     {
         ThemedComboBoxDrawing.DropDownState btnState = ThemedComboBoxDrawing.DropDownState.Normal;
         int rowIndex = e.Style.CellIdentity.RowIndex;
         int colIndex = e.Style.CellIdentity.ColIndex;
 
         bool isHovering = e.Button.IsHovering(rowIndex, colIndex);
         bool isMouseDown = e.Button.IsMouseDown(rowIndex, colIndex);
 
         bool disabled = !e.Style.Clickable;
 
         if (disabled)
         {
             btnState = ThemedComboBoxDrawing.DropDownState.Disabled;
         }
         else if (isMouseDown)
         {
             btnState = ThemedComboBoxDrawing.DropDownState.Pressed;
         }
         else if (isHovering)
         {
             btnState = ThemedComboBoxDrawing.DropDownState.Hot;
         }
 
//Customize the ComboBox Button.   
this.gridGroupingControl1.TableModel.Options.GridVisualStylesDrawing.DrawComboBoxStyle(e.Graphics, e.Button.Bounds, btnState, Color.Gray);
         Bitmap bitmap = new Bitmap(@"..\..\Resources\down.png");
 
        //Customize the icon of ComboBox.
         iconPaint.PaintIcon(e.Graphics, e.Button.Bounds, Point.Empty, bitmap, Color.Black);
         e.Cancel = true;
     }
 }

'Triggering the event.
AddHandler gridGroupingControl1.TableControl.DrawCellButtonBackground, AddressOf TableControl_DrawCellButtonBackground
 
'Event customization.
 Private Sub TableControl_DrawCellButtonBackground(ByVal sender As Object, ByVal e As GridDrawCellButtonBackgroundEventArgs)
     If e.Style.CellType Is GridCellTypeName.ComboBox Then
         Dim btnState As ThemedComboBoxDrawing.DropDownState = ThemedComboBoxDrawing.DropDownState.Normal
         Dim rowIndex As Integer = e.Style.CellIdentity.RowIndex
         Dim colIndex As Integer = e.Style.CellIdentity.ColIndex
 
         Dim isHovering As Boolean = e.Button.IsHovering(rowIndex, colIndex)
         Dim isMouseDown As Boolean = e.Button.IsMouseDown(rowIndex, colIndex)
 
         Dim disabled As Boolean = Not e.Style.Clickable
 
         If disabled Then
             btnState = ThemedComboBoxDrawing.DropDownState.Disabled
         ElseIf isMouseDown Then
             btnState = ThemedComboBoxDrawing.DropDownState.Pressed
         ElseIf isHovering Then
             btnState = ThemedComboBoxDrawing.DropDownState.Hot
         End If
  
'Customize the ComboBox Button. Me.gridGroupingControl1.TableModel.Options.GridVisualStylesDrawing.DrawComboBoxStyle(e.Graphics, e.Button.Bounds, btnState, Color.Gray)
         Dim bitmap As New Bitmap("..\..\Resources\down.png")
         'Customize the icon of ComboBox.
         iconPaint.PaintIcon(e.Graphics, e.Button.Bounds, Point.Empty, bitmap, Color.Black)
         e.Cancel = True
     End If
 End Sub

GridCellRendererBase cellRenderer = this.gridGroupingControl1.TableControl.CellRenderers["ComboBox"];
renderer = (cellRenderer as GridDropDownGridListControlCellRenderer);
//Triggering the event of combobox cell renderer
renderer.ListControlPart.Grid.PrepareViewStyleInfo += new GridPrepareViewStyleInfoEventHandler(Grid_PrepareViewStyleInfo);
 
//Event customization.
void Grid_PrepareViewStyleInfo(object sender, GridPrepareViewStyleInfoEventArgs e)
{
    e.Style.TextColor = Color.White;
 
    if (renderer.ListControlPart.Grid.CurrentCell.RowIndex == e.RowIndex)
    {
        e.Style.BackColor = Color.PaleGreen;
    }
    e.Style.Font.Facename = "Segoe UI";
    e.Style.Borders.Bottom = new GridBorder(GridBorderStyle.Solid, Color.Green);
}

Dim cellRenderer As GridCellRendererBase = Me.gridGroupingControl1.TableControl.CellRenderers("ComboBox")
renderer = (TryCast(cellRenderer, GridDropDownGridListControlCellRenderer))
'Triggering the event of combobox cell renderer
AddHandler renderer.ListControlPart.Grid.PrepareViewStyleInfo, AddressOf Grid_PrepareViewStyleInfo
 
'Event customization.
void Grid_PrepareViewStyleInfo(Object sender, GridPrepareViewStyleInfoEventArgs e)
    e.Style.TextColor = Color.White
 
    If renderer.ListControlPart.Grid.CurrentCell.RowIndex = e.RowIndex Then
        e.Style.BackColor = Color.PaleGreen
    End If
    e.Style.Font.Facename = "Segoe UI"
    e.Style.Borders.Bottom = New GridBorder(GridBorderStyle.Solid, Color.Green)