You can set the StyleUI property of the grid to "Bootstrap" to take advantage of Bootstrap UI theming. Default is "jQueryUI".
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="default.aspx.cs" Inherits="JQSuiteASPNETExample.examples.grid.appearance.bootstrap._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 example with Bootstrap support</title>

    <!-- 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>   
    
     <!-- The Bootstrap default theme, can be any Bootstrap theme -->
    <link rel="stylesheet" href="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css">
    <!-- The jqGrid Bootstrap theme suuport -->
    <link rel="stylesheet" type="text/css" href="/themes/ui.jqgrid-bootstrap.css" />     
        
    <style type="text/css">    
        body, html { font-size: 80%; }
    </style>
</head>


<body>
    <form id="form1" runat="server">  
    
    <br /><br />
        
    <trirand:JQGrid 
        runat="server" 
        ID="JQGrid1" 
        StyleUI="Bootstrap"
        DataSourceID="SqlDataSource1" 
        Width="600px">
        <Columns>
            <trirand:JQGridColumn DataField="OrderID" HeaderText="Order ID" PrimaryKey="True" Width="50" />
            <trirand:JQGridColumn DataField="RequiredDate" DataFormatString="{0:d}">
                <SearchOptions>
                    <trirand:JQGridColumnSearchOption SearchOperation="Contains" />
                </SearchOptions>
            </trirand:JQGridColumn>
            <trirand:JQGridColumn DataField="ShipName" Width="200" />
            <trirand:JQGridColumn DataField="ShipCity" />
            <trirand:JQGridColumn DataField="Freight" />
        </Columns>
    </trirand:JQGrid>

     <asp:SqlDataSource runat="server" ID="SqlDataSource1" 
        ConnectionString="<%$ ConnectionStrings:SQL2008_661086_trirandEntities %>"                 
        SelectCommand="SELECT [OrderID], [RequiredDate], [ShipName], [ShipCity], [Freight] FROM [Orders]">
    </asp:SqlDataSource>  
    
    <br /><br />    
    
        <!-- Needed only for the code tabs below the demo. No need to add it to your code. -->
        <link rel="stylesheet" type="text/css" media="screen" href="http://code.jquery.com/ui/1.12.1/themes/redmond/jquery-ui.css" />
        <trirand:codetabs runat="server" id="tabs"></trirand:codetabs> 
        <!-- Needed only for the code tabs below the demo. No need to add it to your code. --> 
    
    </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.bootstrap
{
    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" />