reStructuredText .. container:: directive is not working

[luator]

I thought I could use the container directive for some customisation of the layout, but for some reason it has no effect.
I am not sure if this is a bug or if I am just missing something.

I am using the latest version of darkslide (installed through pip).

Minimal Example

Test
====

.. container:: foo

   Some content.

   In a container.

This line is not in the container anymore.

Expected Output

...
<section>
    <div class="foo">
        <p>Some content.</p>
        <p>In a container.</p>
    </div>
    <p>This line is not in the container anymore.</p>
</section>
...

Actual Output

...
<section>
    <p>Some content.</p>
    <p>In a container.</p>
    <p>This line is not in the container anymore.</p>
</section>
...