index.template
find
<link rel="stylesheet" type="text/css" href="', $settings['theme_url'], '/css/index', $context['theme_variant'], '.css?fin20" />';
replace with
<link rel="stylesheet" type="text/css" href="', $settings['theme_url'], '/css/index', $context['theme_variant'], '.css?fin20" />
<link rel="stylesheet" type="text/css" href="', $settings['theme_url'], '/css/responsive', $context['theme_variant'], '.css?fin20" />';
find
<a class="', $button['active_button'] ? 'active ' : '', '" href="', $button['href'], '"', isset($button['target']) ? ' target="' . $button['target'] . '"' : '', '>
replace with
<a class="', $button['active_button'] ? 'active ' : '', '" href="', $button['href'], '"', isset($button['target']) ? ' target="' . $button['target'] . '"' : '', '><span class="responsive_menu ', $act, '"></span>
this second one is using most likley place based on default code that is changed.