Customize the text box inside the filter cell

 
private void rgvCompanyList_ViewRowFormatting(object sender, RowFormattingEventArgs e)
        {
            if (e.RowElement is GridFilterRowElement)
            {
                e.RowElement.RowInfo.Height = 40;
                e.RowElement.BorderBoxStyle = BorderBoxStyle.FourBorders;
                e.RowElement.BorderWidth = 4;
                e.RowElement.BorderColor = Color.Red;
            }
}
 

private void rgvCompanyList_ViewCellFormatting(object sender, CellFormattingEventArgs e)
        {
            if (e.CellElement is GridFilterCellElement)
            {
                e.CellElement.DrawBorder = true;
                e.CellElement.BorderBoxStyle = BorderBoxStyle.FourBorders;
                e.CellElement.BorderWidth = 2;
                e.CellElement.BorderColor = Color.Red;
                Font font = new Font(e.CellElement.Font.Name, 9, FontStyle.Bold);
                e.CellElement.Font = font;
                e.CellElement.TextAlignment = ContentAlignment.MiddleCenter;
            }
        }