I need help to create mobile menu

Hi

Currently same menu is showing on desktop and mobile. I want when someone click on icon, a drop-down menu open on mobile device.

Here is the code **Css:** /* New Category menu above header image */ 
.cat-menu { text-align: center; border-bottom: 1px solid #ccc; } .cat-menu ul li { list-style: none; padding: 0 12px; border-right: 2px solid #18c1ee; font-size: 14px; font-weight: 700; text-transform: uppercase; position: relative; display: inline-block; } .cat-menu a:hover, .cat-menu a:focus { color: #18c1ee !important; border-bottom: 2px solid #18c1ee !important; } .cat-menu ul, ol { margin: .1em 0 0.1em 0; padding: 0; }

**Header.php** ---	<div class="cat-menu" ><?php wp_nav_menu ( array ( 'theme_location' => 'cat-menu' )); ?> 

**Function.php** function twentysixteen_register_menu() { register_nav_menu('cat-menu',__('Above the Header')); } add_action('init', 'twentysixteen_register_menu');

Thanks!

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