netbox-community-netbox/netbox/templates/inc/search_panel.html

<div class="panel panel-default">
    <div class="panel-heading">
        <span class="fa fa-search" aria-hidden="true"></span>
        <strong>Search</strong>
    </div>
    <div class="panel-body">
        <form action="." method="get">
            <div class="input-group">
                <input type="text" name="q" class="form-control" placeholder="Search" {% if request.GET.q %}value="{{ request.GET.q }}" {% endif %}/>
                <span class="input-group-btn">
                    <button type="submit" class="btn btn-primary">
                        <span class="fa fa-search" aria-hidden="true"></span>
                    </button>
                </span>
            </div>
        </form>
    </div>
</div>