Template source: partials/searches/_search_form_header.html

<div id="search_form_header" class="input-group navigation_search_bar">
	<div class="input-group search header-search">
		<form method="post" class="autocomplete-header">
			{% csrf_token %}
			<input type="text" id="id_q_header" name="q" class="form-control" autocomplete="off">
			<span class="input-group-addon">				
				<button id="header_search_submit" type="submit">
					<span class="glyphicon glyphicon-search"></span>
				</button>  
			</span>
		</form>
	</div>
</div>