app\templates\collection(4).html

#...
<p id="collection-description">{{ collection.description }}</p>
<p>
    {% if current_user.can(Permission.FOLLOW) and user != current_user %}
        {% if not current_user.is_following_collection(collection) %}
        <a href="{{ url_for('.follow_collection', id=collection.id) }}" class="btn btn-primary">Follow</a>
        {% else %}
        <a href="{{ url_for('.unfollow_collection', id=collection.id) }}" class="btn btn-default">Unfollow</a>
        {% endif %}
    {% endif %}
</p>
#...