JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/jqgrid/4.6.0/css/ui.jqgrid.css">
<script src="https://cdnjs.cloudflare.com/ajax/libs/jqgrid/4.6.0/js/i18n/grid.locale-en.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jqgrid/4.6.0/js/jquery.jqGrid.min.js"></script>
<link rel="stylesheet" href="https://code.jquery.com/ui/1.11.3/themes/smoothness/jquery-ui.css">
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/css/bootstrap.min.css">
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/css/bootstrap-theme.min.css">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/js/bootstrap.min.js"></script>
<button type='button' data-toggle="modal" data-target="#customer-login" data-backdrop="static">Click here</button>

<div class="modal fade" id="customer-login" tabindex="-1" role="dialog" aria-labelledby="customer-login-header" aria-hidden="true">
    <div class="modal-dialog">
        <form action="https://www.mexpro.com/client_login/do/login.mhtml?aff_id=2149" method="POST" name="log-in">
            <div class="modal-content">
                <div class="modal-header">
                    <button type="button" class="close" data-dismiss="modal">x</button>
                    <h2 id="customer-login-header">Customer Login</h2>
                    <p class="hidden-xs">Log in below to receive access to your existing policies and quotes.  The log in information was emailed to your after purchasing your policy or saving a quote.</p>
                </div>
                <div class="modal-body">
                   <div id='error' class='alert alert-warning hide'></div>    
                    <fieldset>
                        <input type="text" class="form-control" id="cl_username" name="username" placeholder="Username?"/>
                        <br/>
                            <input type="password" class="form-control" id="cl_password" name="password"...

JavaScript

$('#SubmitBtn').on('click', function(event){
    var errorDiv = $('#error');
    errorDiv.addClass('hide').empty();
    
    var userName = $('#cl_username').val();
    var password = $('#cl_password').val();
   if ($.trim(userName) == '' || $.trim(password) == '')
   {
     errorDiv.removeClass('hide').append('User Name and Password is required');
     event.preventDefault();
   }
});