<ul class='nav nav-tabs'>
    <li{% if tab == 'details' %} class='active'{% endif %}>
        <a href="{% url 'build-detail' build.id %}">Details</a>
    </li>
    <li{% if tab == 'allocate' %} class='active'{% endif %}>
        <a href="{% url 'build-allocate' build.id %}">Assign Parts</a>
    </li>
</ul>