You can hook client-side events that fire for various dropdownlist events, such as selection, dropdown hide/show, etc. This is achieved through the collection of the JQDropDownList class. Each event is a string pointing to a javascript function that will execute when the event is fired. Each function typically receives two parameters - the item causing the event and the event argument of the browser (client-side event). Some events like Select, etc can be cancelled by returning false from the event handler.
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="default.aspx.cs" Inherits="JQSuiteASPNETExample.examples.dropdownlist.clientevents._default" %>
<%@ Register Assembly="Trirand.Web" TagPrefix="trirand" Namespace="Trirand.Web.UI.WebControls" %>

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
    <title>jqDropDownList for ASP.NET WebForms - Client-Side Events</title>
    <!-- The jQuery UI theme that will be used by the dropdownlist  -->
    <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 dropdownlist needs -->
    <link rel="stylesheet" type="text/css" href="/themes/ui.jqdropdownlist.css" />
    <!-- jQuery runtime minified -->
    <script type="text/javascript" src="/js/jquery-3.2.1.min.js"></script>
    <!-- The jqDropDownList client-side javascript -->
    <script type="text/javascript" src="/js/trirand/jquery.jqDropDownList.min.js"></script>
    <style type="text/css">    
        body, html { font-size: 80%; }
    </style>
</head>
<body>    
    <form id="Form1" runat="server">
    <table cellpadding="10" cellspacing="10">
        <tr>
            <td valign="top">
                <trirand:JQDropDownList 
                    ID="JQDropDownList1"
                    Height="200"
                    Width="150"                    
                    runat="server">
                    <Items>
                        <trirand:JQListItem Text="One" Value="One" />
                        <trirand:JQListItem Text="Two" Value="Two" />
                        <trirand:JQListItem Text="Three" Value="Three" />
                        <trirand:JQListItem Text="Four" />
                        <trirand:JQListItem Text="Five" />
                        <trirand:JQListItem Text="Six" />
                        <trirand:JQListItem Text="Seven" />
                        <trirand:JQListItem Text="Eight" />
                        <trirand:JQListItem Text="Nine" />
                        <trirand:JQListItem Text="Ten" />
                    </Items>
                    <ClientSideEvents
                        Show="handleShow"
                        Hide="handleHide"
                        MouseOver="handleMouseOver"
                        MouseOut="handleMouseOut"
                        Select="handleSelect"
                        Initialized="handleInitialized"
                        KeyDown="handleKeyDown"                    
                    />
                </trirand:JQDropDownList>
            </td>   
            <td valign="top" style="width:300px; height: 300px;">                
                <div id="eventLog" style="height:300px; overflow:auto; font-size:110%; font-family:Tahoma" />
            </td>                 
        </tr>
    </table>   
    
    <br /><br /><br />
    <br /><br /><br />  
    
    <script type="text/javascript">
    
    function handleInitialized(dropDown) {
        write("DropDownList initialized.");
    }
    
    function handleKeyDown(dropDown, events) {
        write(events.keyCode + " is the keyCode of the key pressed.");
    }
    
    function handleShow() {        
        write("DropDown shown.");
    }
    
    function handleHide() {                
        write("DropDown hidden.");
    }
    
    function handleMouseOut(item, event) {
        var dropDown = $("#<%= JQDropDownList1.ClientID %>").getDropDownListInstance();
        var itemOptions = dropDown.getItemOptions(item);        
        writeLine(itemOptions.text, "<b>MouseOut</b> fired");
    }
    
    function handleMouseOver(item, event) {
        var dropDown = $("#<%= JQDropDownList1.ClientID %>").getDropDownListInstance();
        var itemOptions = dropDown.getItemOptions(item);
        
        writeLine(itemOptions.text, "<b>MouseOver</b> fired");
    }
    
    function handleSelect(item, event) {
        var dropDown = $("#<%= JQDropDownList1.ClientID %>").getDropDownListInstance();
        var itemOptions = dropDown.getItemOptions(item);             
        
        if (itemOptions.text == "Two") {
            writeLine(itemOptions.text," : <b>cannot be selected</b>");
            return false;
        }
        
        writeLine(itemOptions.text, " : <b>Select</b> fired");
    }
    
    function writeLine(itemText, message) {
        var currentText = $("#eventLog").html();
        $("#eventLog").html(message + " for item <b>" + itemText + "</b><br>" + currentText);
    }
    
    function write(message) {
        var currentText = $("#eventLog").html();
        $("#eventLog").html("<b>" + message + "</b><br>" + currentText);
    }
    
    </script>

    
    <div>
        <trirand:codetabs runat="server" ID="tabs"></trirand:codetabs>
    </div>
    
    </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.dropdownlist.clientevents
{
    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" />