You can add custom toolbar buttons to the grid using the ToolBarSettings.CustomButtons collection. A custom button has many properties, like Text, ToolTip, ButtonIcon,Position and OnClick client-side event handler - the name of the client-side javascript function that will fire on clicking the button. ButtonIcon is the name of the CSS class that will be applied to the button that holds image information (as per ThemeRoller specs).

Please, refer to the Controller tab for details on setting up a custom button and to the View tab for javascript code details.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI.WebControls;
using Trirand.Web.Mvc;

namespace MVCDemo.Models
{
    public class OrdersJqGridModel
    {
        public JQGrid OrdersGrid { get; set; }

        public OrdersJqGridModel()
        {
            OrdersGrid = new JQGrid
            {
                Columns = new List<JQGridColumn>()
                {
                    new JQGridColumn 
                    {
                        // Always set PrimaryKey for Add,Edit,Delete operations
                        // If not set, the first column will be assumed as primary key
                        DataField = "OrderID",                                        
                        PrimaryKey = true,
                        Editable = false,
                        Width = 50,
                        DataType = typeof(int)
                    },                                    
                    new JQGridColumn 
                    { 
                        DataField = "CustomerID", 
                        Editable = true,
                        Width = 100,
                        DataType = typeof(string),
                        ShowColumnMenu = true,
                    },
                    new JQGridColumn 
                    { 
                        DataField = "OrderDate",                                                         
                        Editable = true,
                        Width = 100, 
                        DataFormatString = "{0:yyyy/MM/dd}",
                        DataType = typeof(DateTime),
                        ShowColumnMenu = true,
                    },
                    new JQGridColumn
                    { 
                        DataField = "Freight", 
                        Editable = true,
                        Width = 75,
                        DataType = typeof(double),
                        ShowColumnMenu = true
                    },
                    new JQGridColumn 
                    { 
                        DataField = "ShipName",
                        Editable =  true,
                        Width = 150,
                        DataType = typeof(string)
                    }
                },
                
                Width = Unit.Pixel(640),
                Height = Unit.Pixel(250),
                
                ToolBarSettings = new ToolBarSettings
                {
                    ShowRefreshButton = true
                }
            };  
        }        
    }
}
@model MVCDemo.Models.OrdersJqGridModel
@using Trirand.Web.Mvc
@using MVCDemo.Models

<!DOCTYPE html>
<html lang="en-us">
<head>
    <meta charset="utf-8">
    <title>jqGrid for ASP.NET MVC - Custom ToolBar Button</title>    
    <!-- jQuery runtime minified -->
    <script src="~/Scripts/jquery-3.2.1.min.js" type="text/javascript"></script>
    <!-- The jqGrid localization file we need, English in this case -->
    <script type="text/javascript" src="~/Scripts/trirand/i18n/grid.locale-en.js"></script>
    <!-- The jqGrid client-side javascript -->
    <script type="text/javascript" src="~/Scripts/trirand/jquery.jqGrid.min.js"></script>
    <!-- The jQuery UI theme that will be used by the grid. -->
    <link rel="stylesheet" type="text/css" href="http://code.jquery.com/ui/1.12.1/themes/redmond/jquery-ui.css" />
    <!-- The jQuery UI theme extension jqGrid needs -->    
    <link rel="stylesheet" type="text/css" href="~/Content/themes/ui.jqgrid.css" />
</head>
<body>
    <div>           
        @Html.Trirand().JQGrid(Model.OrdersGrid, "CustomButtonGrid")
    </div>
    <br /><br />
    <div>
                  
    </div>
    
    <script type="text/javascript">
    
        function mailButtonClicked()
        {
            alert("You have clicked a custom button.");
        }

        function updateButtonClicked() {
            alert("You have clicked the Update button.");
        }
    
    </script>
    
</body>
</html>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using MVCDemo.Models;
using Trirand.Web.Mvc;

namespace MVCDemo.Controllers.Grid
{
    public partial class GridController : Controller
    {
        // This is the default action for the View. Use it to setup your grid Model.
        public ActionResult FunctionalityCustomButton()
        {
            // Get the model (setup) of the grid defined in the /Models folder.
            var gridModel = new OrdersJqGridModel();
            var grid = gridModel.OrdersGrid;

            // Setting the DataUrl to an action (method) in the controller is required.
            // This action will return the data needed by the grid            
            grid.DataUrl = Url.Action("FunctionalityCustomButton_DataRequested");

            // add a new custom button to the toolbar
            grid.ToolBarSettings.CustomButtons.Add(
                new JQGridToolBarButton
                {
                    Text = "Send",
                    ToolTip = "Send Mail",
                    ButtonIcon = "ui-icon-mail-closed",
                    Position = ToolBarButtonPosition.Last,
                    OnClick = "mailButtonClicked"
                }
            );

            grid.ToolBarSettings.CustomButtons.Add(
               new JQGridToolBarButton
               {
                   Text = "Update",
                   ToolTip = "Write an Update",
                   ButtonIcon = "ui-icon-pencil",
                   Position = ToolBarButtonPosition.Last,
                   OnClick = "updateButtonClicked"
               }
           );

            grid.ToolBarSettings.ToolBarPosition = ToolBarPosition.TopAndBottom;

            // Pass the custmomized grid model to the View
            return View(gridModel);
        }

        // This method is called when the grid requests data. You can choose any method to call
        // by setting the JQGrid.DataUrl property
        public JsonResult FunctionalityCustomButton_DataRequested()
        {
            // Get both the grid Model and the data Model
            // The data model in our case is an autogenerated linq2sql database based on Northwind.
            var gridModel = new OrdersJqGridModel();
            var northWindModel = new NorthwindDataContext();

            // return the result of the DataBind method, passing the datasource as a parameter
            // jqGrid for ASP.NET MVC automatically takes care of paging, sorting, filtering/searching, etc
            return gridModel.OrdersGrid.DataBind(northWindModel.Orders);
        }
    }
}
Switch theme:


Theming is based on the very popular jQuery ThemeRoller standard. This is the same theming mechanism used by jQuery UI and is now a de-facto standard for jQuery based components. The benefits of using ThemeRoller are huge. We can offer a big set of ready to use themes created by professional designers, including Windows-like themes (Redmond), Apple-like theme (Cupertino), etc. In addition to that any jQuery UI controls on the same page will pick the same theme.

Last, but not least, you can always roll your own ThemeRoller theme, using the superb Theme Editor

To use a theme, simply reference 2 Css files in your Html <head> section - the ThemeRoller theme you wish to use, and the jqGrid own ThemeRoller Css file. For example (Redmond theme):

<link rel="stylesheet" type="text/css" media="screen" href="/themes/redmond/jquery-ui-1.8.2.custom.css" />
<link rel="stylesheet" type="text/css" media="screen" href="/themes/ui.jqgrid.css" />