Copy whole code as is save as .html and run
it will work only on IOS devices
on Desktop (outlook, Gmail, Yahoo) by default it's open
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN">
<html>
<head>
<title></title>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<meta name="x-apple-disable-message-reformatting">
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, minimum-scale=1, user-scalable=no">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<!--[if IE]>
<style>
sup,sub { font-size: 80% !important; display:inline !important; line-height:1em !important; vertical-align:top !important;}
sub { vertical-align:bottom !important; }
</style>
<![endif]-->
<!--[if gte mso 12]>
<style>
sup,sub{ font-size: 100% !important; vertical-align:top !important; display:inline !important;}
sub { mso-text-raise:-0.15em; }
</style>
<![endif]-->
<style>table{border-collapse:collapse}@media screen and (max-width: 480px), yahoo and (max-width: 480px), print and (max-width: 552px){*{box-sizing:border-box;word-break:break-word;-webkit-text-size-adjust:none;text-size-adjust:none;mso-line-height-rule:exactly}html,body{width:100vw}body{margin:0px !important;padding:0px !important;font-family:Arial,Helvetica,sans-serif;color:#555;background:#fff !important}.mobile_padding{padding-left:6%!important;padding-right:6%!important}.wrapper{background:#fff !important}.body_table{box-shadow:none !important}.device_width{width:100% !important;display:table}.brand{padding-top:20px}.preheader_sec{padding-bottom:0px !important}.brand img{max-width:150px}}.expanded-row-content{border-top:none;display:grid;grid-column:1/-1;justify-content:flex-start;color:#AEB1B3;font-size:13px;background-color:#fff}.hide-row{display:none}</style>
<style type="text/css">.ReadMsgBody{width:100%}.ExternalClass{width:100%}.ExternalClass *{line-height:100%}div,p,a,li,td{-webkit-text-size-adjust:none;-ms-text-size-adjust:none}TD IMG{display:block;border:0}table{border-collapse:collapse;mso-table-lspace:0pt;mso-table-rspace:0pt}table td{border-collapse:collapse}a:link{color:#000001;text-decoration:none}a:active{color:#000001;text-decoration:none}a:visited{color:#000001;text-decoration:none}a:hover{color:#000001;text-decoration:none}textarea{resize:none}textarea:focus,input:focus{outline:none}body{margin:0;font-family:Arial,Helvetica,sans-serif}.appleLinks a{color:inherit !important;text-decoration:none}@-ms-viewport{width:device-width}@media only screen and (max-width: 480px){body[yahoo] .container{width:100% !important}body[yahoo] .mobile-hidden{display:none !important}body[yahoo] .photo{width:100% !important;height:auto !important}body[yahoo] .mobile-padding{padding-right:20px !important;padding-left:20px !important}body[yahoo] .drop{width:100% !important;float:left !important}body[yahoo] .left{float:left !important}body[yahoo] .text-left{text-align:left !important}body[yahoo] .logo{width:100px !important;height:auto !important}body[yahoo] .show{display:block !important;margin:0 !important;padding:0 !important;overflow:visible !important;width:100% !important;max-height:inherit !important}body[yahoo] .footer-logo{width:95px !important;height:auto !important}body[yahoo] .padding15{padding-top:15px !important;padding-bottom:15px !important}body[yahoo] .padding20{padding-top:20px !important;padding-bottom:20px !important}body[yahoo] .padding0{padding:0 !important}body[yahoo] .paddingtop0{padding-top:0px !important}body[yahoo] .paddingtop10{padding-top:10px !important}body[yahoo] .paddingtop15{padding-top:15px !important}body[yahoo] .paddingtop20{padding-top:20px !important}body[yahoo] .paddingright20{padding-right:20px !important}body[yahoo] .paddingbottom0{padding-bottom:0px !important}body[yahoo] .paddingbottom10{padding-bottom:10px !important}body[yahoo] .paddingbottom15{padding-bottom:15px !important}body[yahoo] .paddingbottom20{padding-bottom:20px !important}body[yahoo] .paddingleft0{padding-left:0px !important}body[yahoo] .paddingleft20{padding-left:20px !important}body[yahoo] .cta{width:100% !important}body[yahoo] .hidden{display:none !important}body[yahoo] .center{margin:0 auto}body[yahoo] .text-center{text-align:center !important}body[yahoo] .ctafix{line-height:18px !important;padding-top:10px !important;padding-bottom:10px !important}body[yahoo] .font20{font-size:20px !important;line-height:24px !important}body[yahoo] .font15{font-size:15px !important;line-height:19px !important}body[yahoo] .font18{font-size:18px !important;line-height:22px !important}body[yahoo] .font14{font-size:14px !important;line-height:18px !important}body[yahoo] .font13{font-size:13px !important;line-height:17px !important}body[yahoo] .width50{width:50px !important;height:auto !important}body[yahoo] .width70{width:70px !important;height:auto !important}body[yahoo] .width15{width:15px !important;height:auto !important}}@media yahoo, only screen and (min-width:0){body[yahoo] .mj-accordion-element{display:block}input.mj-accordion-checkbox,.mj-accordion-less{display:none !important}input.mj-accordion-checkbox+* .mj-accordion-title{cursor:pointer;touch-action:manipulation;-webkit-user-select:none;-moz-user-select:none;user-select:none}input.mj-accordion-checkbox+* .mj-accordion-content{overflow:hidden;display:none}input.mj-accordion-checkbox+* .mj-accordion-more{display:block !important}input.mj-accordion-checkbox:checked+* .mj-accordion-content{display:block}input.mj-accordion-checkbox:checked+* .mj-accordion-more{display:none !important}input.mj-accordion-checkbox:checked+* .mj-accordion-less{display:block !important}}</style>
</head>
<body bgcolor="#efefef" class="body_full" style="padding:0; margin:0px;">
<table class="wrapper" width="100%" height="100%" cellspacing="0" cellpadding="0" border="0" align="center" style="min-width:100%; min-height:100%; background-color:#efefef;">
<tbody>
<tr>
<td class="noTopPadding pb0" style="padding-top:30px; padding-bottom:30px;" align="center">
<center>
<table class="body_table device_width" width="660" cellspacing="0" cellpadding="0" border="0" align="center" style="margin:0 auto; background-color:#ffffff; ">
<tr>
<td>
<!-- Accordion Section starts -->
<div style="">
<!--[if mso | IE]>
<table
align="center" border="0" cellpadding="0" cellspacing="0" class="" style="width:660;" width="660"
>
<tr>
<td style="line-height:0px;font-size:0px;mso-line-height-rule:exactly;">
<![endif]-->
<div style="background:#ffffff;background-color:#ffffff;margin:0px auto;max-width:660;">
<table align="center" border="0" cellpadding="0" cellspacing="0" role="presentation" style="background:#ffffff;background-color:#ffffff;width:100%;">
<tbody>
<tr>
<td class="mobile_padding" style="direction:ltr;font-size:0px;padding:0px 33px 0px 33px;text-align:center;">
<!--[if mso | IE]>
<table role="presentation" border="0" cellpadding="0" cellspacing="0">
<tr>
<td
class="" style="vertical-align:top;width:660;"
>
<![endif]-->
<div class="mj-column-per-100 mj-outlook-group-fix" style="font-size:0px;text-align:left;direction:ltr;display:inline-block;vertical-align:top;width:100%;">
<table border="0" cellpadding="0" cellspacing="0" role="presentation" style="vertical-align:top;" width="100%">
<tr>
<td style="font-size:0px;padding:1px;word-break:break-word;">
<table cell-spacing="0" cell-padding="0" class="mj-accordion" style="width:100%;border-collapse:collapse;border:none;border-bottom:none;font-family:Ubuntu, Helvetica, Arial, sans-serif;">
<tbody>
<tr>
<td style="padding:0px;">
<label class="mj-accordion-element" style="font-size:13px;">
<!--[if !mso | IE]><!-->
<input class="mj-accordion-checkbox" type="checkbox" style="display:none;" />
<!--<![endif]-->
<div>
<div class="mj-accordion-title">
<table cell-spacing="0" cell-padding="0" style="width:100%;border-bottom:none;background-color:#f0efef;">
<tbody>
<tr>
<td class="fs14" style="width:100%;background-color:#f0efef;color:#00a160;font-size:20px;font-family:Arial, Helvetica, sans-serif;padding:5px 10px; line-height:25px"> <b>Click here to check accordion functionality</b></td>
<!--[if !mso | IE]><!-->
<td class="mj-accordion-ico" style="padding:4px 10px 4px 5px;background:#f0efef;vertical-align:middle;">
<span class="mj-accordion-more" style="display:none;width:18px;height:18px;font-size:20px; line-height:25px;font-family:Arial, Helvetica, sans-serif;color:#231F20;">+</span>
<span class="mj-accordion-less" style="display:none;width:18px;height:18px;font-size:20px; line-height:25px;font-family:Arial, Helvetica, sans-serif;color:#231F20;">-</span>
</td>
<!--<![endif]-->
</tr>
</tbody>
</table>
</div>
<div class="mj-accordion-content">
<table cell-spacing="0" cell-padding="0" style="width:100%;border-bottom:none;">
<tbody>
<tr>
<td class="fs11" align="left" valign="top" style="font-size:12px; line-height:15px;font-family:Arial, Helvetica, sans-serif;color:#231F20;padding:7px 7px 20px 7px;text-align: justify;">Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.
</td>
</tr>
</tbody>
</table>
</div>
</div>
</label>
</td>
</tr>
</tbody>
</table>
</td>
</tr>
</table>
</div>
<!--[if mso | IE]>
</td>
</tr>
</table>
<![endif]-->
</td>
</tr>
</tbody>
</table>
</div>
<!--[if mso | IE]>
</td>
</tr>
</table>
<![endif]-->
</div>
<!-- Accordion Section ends -->
</td>
</tr>
</table>
</center>
</td>
</tr>
</tbody>
</table>
</body>
</html>
CSS
orJavaScript
for accordion. Example: w3schools.com/tags/tryit.asp?filename=tryhtml5_summary – Sushi