JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html>
    <head>
        <title>jQM Complex Demo</title>
        <meta http-equiv='Content-Type' content='text/html; charset=utf-8'/>
        <meta name="viewport" content="width=device-width; initial-scale=1.0; maximum-scale=1.0; minimum-scale=1.0; user-scalable=no; target-densityDpi=device-dpi"/>
        <link rel="stylesheet" href="http://code.jquery.com/mobile/1.4.2/jquery.mobile-1.4.2.min.css" /> 
        <!--<script src="http://code.jquery.com/jquery-1.10.1.min.js"></script>-->
        <script src="http://code.jquery.com/mobile/1.4.2/jquery.mobile-1.4.2.min.js"></script>    
    </head>
    <body>     
        <div data-role="page" id="index" data-theme="a" >
            <div data-role="header">
                <h3>
                    First Page
                </h3>
                <a href="#second" class="ui-btn-right">Next</a>
            </div>
            
            <div data-role="content">
                <a href="#help-dialog" data-rel="popup">Open Popup</a>
                <div data-role="popup"id="help-dialog" data-overlay-theme="a" data-theme="a" data-dismissible="false" data-transition="none" data-position-to="window">
                    <div data-role="header" data-theme="a" class="ui-corner-top">
                        <h1>Popup</h1>
                        
                    </div>
                    <div data-role="content" data-theme="d" class="ui-corner-bottom ui-content">
                        <h3 class="ui-title">Focused Field</h3>
                        
                        <p>
                            <input type="text" id="popup_input" />
                        </p> <a href="#" data-role="button"data-rel="back">Close</a>
                        
                    </div>                    
                </div>              
            </div>
            
            <div data-role="footer" data-position="fixed">
                
            </div>
        </div> 
    </body>
</html>

JavaScript

$(document).on('pageshow', '#index', function(){ 
    var content_width = $.mobile.activePage.find("div[data-role='content']:visible:visible").outerWidth();
    $('#help-dialog').css({'width':content_width*0.8});
});