I dont have modifications. I added now just for text align.
The original:
<?php
/**
* @package HikaShop for Joomla!
* @version 5.0.3
* @author hikashop.com
* @copyright (C) 2010-2024 HIKARI SOFTWARE. All rights reserved.
* @license GNU/GPLv3 http://www.gnu.org/licenses/gpl-3.0.html
*/
defined('_JEXEC') or die('Restricted access');
?><table class="w600" border="0" cellspacing="0" cellpadding="0" width="600" style="margin:0px;font-family: Arial, Helvetica, sans-serif;font-size:12px;line-height:18px;">
<tr>
<td class="w20" width="20"></td>
<td class="w560 pict" style="text-align:left; color:#575757" width="560">
<div id="title" style="font-family: Arial, Helvetica, sans-serif;font-size:12px;line-height:18px;">
<img src="{VAR:LIVE_SITE}media/com_hikashop/images/icons/icon-48-order.png" border="0" alt="" style="float:left;margin-right:4px;"/>
<h1 class="hika_template_color" style="font-size:16px;font-weight:bold; border-bottom:1px solid #ddd; padding-bottom:10px">
{TXT:ORDER_TITLE}
</h1>
<h2 class="hika_template_color" style="font-size:12px;font-weight:bold; padding-bottom:10px">
{TXT:ORDER_CREATED}
</h2>
</div>
</td>
<td class="w20" width="20"></td>
</tr>
<tr>
<td class="w20" width="20"></td>
<td style="border:1px solid #adadad;background-color:#ffffff;">
<div class="w550" width="550" id="content" style="font-family: Arial, Helvetica, sans-serif;font-size:12px;line-height:18px;margin-left:5px;margin-right:5px;">
<p>
<h3 style="color:#393939 !important; font-size:14px; font-weight:normal; font-weight:bold;margin-bottom:0px;padding:0px;">{TXT:HI_CUSTOMER}</h3>
{TXT:ORDER_BEGIN_MESSAGE}
</p>
<table class="w550" border="0" cellspacing="0" cellpadding="0" width="550" style="margin-top:10px;font-family: Arial, Helvetica, sans-serif;font-size:12px;line-height:18px;">
<tr>
<!--{IF:BILLING_ADDRESS}--><td class="hika_template_color" style="font-size:12px;font-weight:bold;">{TXT:BILLING_ADDRESS}</td><!--{ENDIF:BILLING_ADDRESS}-->
<!--{IF:SHIPPING}--><!--{IF:SHIPPING_ADDRESS}--><td class="hika_template_color" style="font-size:12px;font-weight:bold;">{TXT:SHIPPING_ADDRESS}</td><!--{ENDIF:SHIPPING_ADDRESS}--><!--{ENDIF:SHIPPING}-->
</tr>
<tr>
<!--{IF:BILLING_ADDRESS}--><td>{VAR:BILLING_ADDRESS}</td><!--{ENDIF:BILLING_ADDRESS}-->
<!--{IF:SHIPPING}--><!--{IF:SHIPPING_ADDRESS}--><td>{VAR:SHIPPING_ADDRESS}</td><!--{ENDIF:SHIPPING_ADDRESS}--><!--{ENDIF:SHIPPING}-->
</tr>
</table>
<h1 class="hika_template_color" style="font-size:16px;font-weight:bold;border-bottom:1px solid #ddd;padding-top:10px;padding-bottom:10px;">
{TXT:SUMMARY_OF_YOUR_ORDER}
</h1>
<!--{START:VENDOR_LINE}-->
<!--{IF:VENDOR_CONTENT}-->{VAR:VENDOR_CONTENT}<!--{ENDIF:VENDOR_CONTENT}-->
<table class="w550" border="0" cellspacing="0" cellpadding="0" width="550" style="margin-top:10px;margin-bottom:10px;font-family: Arial, Helvetica, sans-serif;font-size:12px;line-height:18px;">
<tr>
<td class="hika_template_color" style="border-bottom:1px solid #ddd;padding-bottom:3px;text-align:left;font-size:12px;font-weight:bold;">{TXT:PRODUCT_NAME}</td>
{TXT:CUSTOMFIELD_NAME}
<td class="hika_template_color" style="border-bottom:1px solid #ddd;padding-bottom:3px;text-align:right;font-size:12px;font-weight:bold;">{TXT:PRODUCT_PRICE}</td>
<td class="hika_template_color" style="border-bottom:1px solid #ddd;padding-bottom:3px;text-align:right;font-size:12px;font-weight:bold;">{TXT:PRODUCT_QUANTITY}</td>
<td class="hika_template_color" style="border-bottom:1px solid #ddd;padding-bottom:3px;text-align:right;font-size:12px;font-weight:bold;">{TXT:PRODUCT_TOTAL}</td>
</tr>
<!--{START:PRODUCT_LINE}-->
<tr>
<td style="border-bottom:1px solid #ddd;padding-bottom:3px;">
{LINEVAR:PRODUCT_IMG}
{LINEVAR:PRODUCT_NAME}<!--{IF:ORDER_PRODUCT_CODE}--> {LINEVAR:PRODUCT_CODE}<!--{ENDIF:ORDER_PRODUCT_CODE}-->
{LINEVAR:PRODUCT_DOWNLOAD}
{LINEVAR:PRODUCT_DETAILS}
</td>
{LINEVAR:CUSTOMFIELD_VALUE}
<td style="border-bottom:1px solid #ddd;padding-bottom:3px;text-align:right">{LINEVAR:PRODUCT_PRICE}</td>
<td style="border-bottom:1px solid #ddd;padding-bottom:3px;text-align:center">{LINEVAR:PRODUCT_QUANTITY}</td>
<td style="border-bottom:1px solid #ddd;padding-bottom:3px;text-align:right">{LINEVAR:PRODUCT_TOTAL}</td>
</tr>
<!--{END:PRODUCT_LINE}-->
<!--{START:ORDER_FOOTER}-->
<tr>
<td class="hika_template_color {LINEVAR:CLASS}_label" colspan="{TXT:FOOTER_COLSPAN}" style="text-align:right;font-size:12px;font-weight:bold;">{LINEVAR:NAME}</td>
<td class="{LINEVAR:CLASS}_value" style="text-align:right">{LINEVAR:VALUE}</td>
</tr>
<!--{END:ORDER_FOOTER}-->
</table>
<!--{END:VENDOR_LINE}-->
<!--{IF:PAYMENT}-->
<p>
<span class="hika_template_color" style="font-size:12px;font-weight:bold;">{TXT:PAYMENT_METHOD} :</span> {VAR:PAYMENT}
</p>
<!--{ENDIF:PAYMENT}-->
<!--{IF:SHIPPING}-->
<p>
<span class="hika_template_color" style="font-size:12px;font-weight:bold;">{TXT:HIKASHOP_SHIPPING_METHOD} :</span> {VAR:SHIPPING}
</p>
<!--{ENDIF:SHIPPING}-->
<!--{IF:ORDER_SUMMARY}-->
<h1 class="hika_template_color" style="font-size:16px;font-weight:bold;border-bottom:1px solid #ddd;padding-top:10px;padding-bottom:10px;">
{TXT:ADDITIONAL_INFORMATION}
</h1>
<p style="border-bottom:1px solid #ddd;padding-bottom:10px;">
{VAR:ORDER_SUMMARY}
</p>
<!--{ENDIF:ORDER_SUMMARY}-->
<p>
{TXT:ORDER_END_MESSAGE}
</p>
</div>
</td>
<td class="w20" width="20"></td>
</tr>
</table>
Now I changed only
<td style="border-bottom:1px solid #ddd;padding-bottom:3px;text-align:center">{LINEVAR:PRODUCT_QUANTITY}</td>
So original code is making problem with email readability. With that override is better, but you can design emails beter.