You can group grid headers into different master groups, so that they visually appear in the same parent group - group hierarchy. The API for that is simple just add any number of CoreGridHeaderGroup instances to the HeaderGroups collection of the grid model.

Each header group has the following properties:

StartColumnName - The name (DataField) of the column from which the grouping header begins, inclusive.
NumberOfColumns - The number of columns that are included in this group. Note that the number starts from the startColumnName. If the column is hidden, it is skipped and as a result the group does not contain the field, but the method counts it.
TitleText - The text for the title of the group. The text can contain html tags.

using Microsoft.AspNetCore.Http;
using System;
using System.Collections.Generic;
using Trirand.Web.Core;

namespace CoreDemo.Models
{
    public class OrdersJqGridModel
    {
        public CoreGrid OrdersGrid { get; set; }

        public OrdersJqGridModel(HttpContext context)
        {
            OrdersGrid = new CoreGrid(context)
            {
                Columns = new List<CoreColumn>()
                {
                    new CoreColumn
                    {
                        // 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 CoreColumn
                    {
                        DataField = "CustomerId",
                        Editable = true,
                        Width = 100,
                        DataType = typeof(string),

                    },
                    new CoreColumn
                    {
                        DataField = "OrderDate",
                        Editable = true,
                        Width = 100,
                        DataFormatString = "{0:yyyy/MM/dd}",
                        DataType = typeof(DateTime)
                    },
                    new CoreColumn
                    {
                        DataField = "Freight",
                        Editable = true,
                        Width = 75,
                        DataType = typeof(double)
                    },
                    new CoreColumn
                    {
                        DataField = "ShipName",
                        Editable =  true,
                        Width = 150,
                        DataType = typeof(string)
                    }
                },

                Width = "640",
                Height = "250",
                
                ToolBarSettings = new ToolBarSettings
                {
                    ShowRefreshButton = true
                }
            };  
        }        
    }
}
@model CoreDemo.Models.OrdersJqGridModel
@using Trirand.Web.Core
@using CoreDemo.Models;

<!DOCTYPE html>
<html lang="en-us">
<head>
    <meta charset="utf-8">
    <title>jqGrid for ASP.NET Core - Header Groups</title>
    <!-- jQuery runtime minified -->
    <script src="~/js/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="~/js/trirand/i18n/grid.locale-en.js"></script>
    <!-- The jqGrid client-side javascript -->
    <script type="text/javascript" src="/js/trirand/coregrid.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="~/css/trirand/coregrid.css" />   
</head>
<body>
    <div>           
        @Html.Trirand().CoreGrid(Model.OrdersGrid, "OrdersGrid")
    </div>
    <br /><br />
    <div>
        @await Component.InvokeAsync("CodeTabs", new { product = "grid", example = "appearanceheadergroups" })          
    </div>    
</body>
</html>
using Microsoft.AspNetCore.Mvc;
using CoreDemo.Models;
using Trirand.Web.Core;

namespace CoreDemo.Controllers.Grid
{
    public partial class GridController : Controller
    {
        // This is the default action for the View. Use it to setup your grid Model.
        public ActionResult AppearanceHeaderGroups()
        {
            // Get the model (setup) of the grid defined in the /Models folder.
            var gridModel = new OrdersJqGridModel(HttpContext);
            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("AppearanceHeaderGroups_DataRequested");
            grid.Width = "600";           

            // Add a header group for two columns - CustomerId and OrderDate
            grid.HeaderGroups.Add(
                new CoreGridHeaderGroup
                {
                    StartColumnName = "CustomerId",
                    NumberOfColumns = 2,
                    TitleText = "General Info"
                }
            );

            // Add a header group for two columns - Freight and ShipName
            grid.HeaderGroups.Add(
                new CoreGridHeaderGroup
                {
                    StartColumnName = "Freight",
                    NumberOfColumns = 2,
                    TitleText = "Secondary Details"
                }
            );
            
            // 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 CoreGrid.DataUrl property
        public JsonResult AppearanceHeaderGroups_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(HttpContext);
            var northWindModel = new NorthWind();

            // return the result of the DataBind method, passing the datasource as a parameter
            // jqGrid for ASP.NET Core 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/coregrid.css" />