You can group the headers of grid columns into different master groups, so that they visually appear in the same parent group. The API for that is simple just add any number of JQGridHeaderGroup 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 begin, including the same field
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 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

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="default.aspx.cs" Inherits="JQSuiteASPNETExample.examples.grid.appearance.headergroups._default" %>
<%@ Register Assembly="Trirand.Web" TagPrefix="trirand" Namespace="Trirand.Web.UI.WebControls" %>

<!DOCTYPE html>
<html lang="en-us">
<head id="Head1" runat="server">
    <meta charset="utf-8">
    <title>jqGrid ASP.NET WebForms - Grouped Headers</title>
    <!-- The jQuery UI theme that will be used by the grid -->
    <link rel="stylesheet" type="text/css" media="screen" 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" media="screen" href="/themes/ui.jqgrid.css" />
    <!-- jQuery runtime minified -->
    <script src="/js/jquery-3.2.1.min.js" type="text/javascript"></script>
    <!-- The localization file we need, English in this case -->
    <script src="/js/trirand/i18n/grid.locale-en.js" type="text/javascript"></script>
    <!-- The jqGrid client-side javascript -->
    <script src="/js/trirand/jquery.jqGrid.min.js" type="text/javascript"></script>
    
    <style type="text/css">
        body, html { font-size: 80%; }
    </style>
</head>
<body>
    <form id="form1" runat="server">
    
    <asp:SqlDataSource runat="server" ID="SqlDataSource1" ConnectionString="<%$ ConnectionStrings:SQL2008_661086_trirandEntities %>"
        SelectCommand="SELECT [CustomerID], [CompanyName], [Phone], [City], [PostalCode] FROM [Customers]">
    </asp:SqlDataSource>
    
    <trirand:JQGrid ID="JQGrid1" runat="server" Width="600px" DataSourceID="SqlDataSource1">
        <Columns>
            <trirand:JQGridColumn DataField="CustomerID" Editable="false" PrimaryKey="true" Frozen="true" />
            <trirand:JQGridColumn DataField="CompanyName" Editable="true" Frozen="true" />
            <trirand:JQGridColumn DataField="Phone" Editable="true" />
            <trirand:JQGridColumn DataField="PostalCode" Editable="true" />
            <trirand:JQGridColumn DataField="City" Editable="true" />
        </Columns>
        <HeaderGroups>
            <trirand:JQGridHeaderGroup StartColumnName="CustomerID" NumberOfColumns="2" TitleText="General Info" />
            <trirand:JQGridHeaderGroup StartColumnName="Phone" NumberOfColumns="2" TitleText="Secondary Details" />
        </HeaderGroups>
    </trirand:JQGrid>
    
    <br />
    <br />
    <trirand:codetabs runat="server" ID="tabs"></trirand:codetabs>
    </form>
</body>
</html>
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace JQSuiteASPNETExample.examples.grid.appearance.headergroups
{
    public partial class _default : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {

        }
    }
}
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" />