netbox/netbox/templates/dcim/inc/device_import_header.html

<ul class="nav nav-tabs" style="margin-bottom: 20px">
    <li role="presentation"{% if not active_tab %} class="active"{% endif %}><a href="{% url 'dcim:device_import' %}">Racked Devices</a></li>
    <li role="presentation"{% if active_tab == 'child_import' %} class="active"{% endif %}><a href="{% url 'dcim:device_import_child' %}">Child Devices</a></li>
</ul>