That is going to depend on your skin. You are using ideal_comfort so I would make all the changes in that skin directory. You should be a able to copy the code below, and simply paste it into a new template file that you create.
In this case I created: /ideal_responsive/customer/categories.tpl
You would likely create: /ideal_comfort/customer/categories.tpl
I took some time and tested this out, for now you can see it working at my test site:
http://trainingpen.com/
I've modified the script to show and hide the div, clicking the link will expand and collapse. I also commented out the unnecessary part that hid other divs.
Code:
{*
df14bc9e9dec4a3332552facb2c31eaaf22d39a2, v5 (xcart_4_4_2), 2010-12-17 15:12:37, categories.tpl, aim
vim: set ts=2 sw=2 sts=2 et:
*}
<script type="text/javascript">
{literal}
$(document).ready(function() {
$('a.title').click(function() {
var correspondingDiv = $(this).parent().next('div');
if (!correspondingDiv.is(':hidden')) {
correspondingDiv.hide(150);
return;
}
// hide other divs
//$('.workdiv').hide(150);
// show this one
correspondingDiv.toggle(150);
});
});
{/literal}
</script>
<div>
<a href="#" id="1" class="title" name="1"><h2>Expand Categories</h2></a>
</div>
<div id="workdiv1" class="workdiv" style="display:none">
{if $categories_menu_list ne '' or $fancy_use_cache}
{capture name=menu}
{if $active_modules.Flyout_Menus}
{include file="modules/Flyout_Menus/categories.tpl"}
{assign var="additional_class" value="menu-fancy-categories-list"}
{else}
<ul>
{foreach from=$categories_menu_list item=c name=categories}
<li{interline name=categories}><a href="home.php?cat={$c.categoryid}" title="{$c.category|escape}">{$c.category|amp}</a></li>
{/foreach}
</ul>
{assign var="additional_class" value="menu-categories-list"}
{/if}
{/capture}
{include file="customer/menu_dialog.tpl" title=$lng.lbl_categories content=$smarty.capture.menu}
{/if}
</div>
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mike@babymonkeystudios.com