Include only current category?

I’m trying to figure out if Collapsing Archives in some way could dynamically include the category which the user is currently viewing.

I have tried putting a PHP “get current category name” code snippet into the widget’s “Include these categories” input field. It was a long shot but worth a try.

I then tried to enter the shortcode into the plugin PHP Code Widget to start Collapsing Archives manually and get more control. I’ve tried the following codes but nothing have worked so far.
collapsArch();
<?php collapsArch(); ?>
<script> collapsArch(); </script>

It shouldn’t be this complicated so clearly I’m missing something. Help me, whoever, you’re my only hope!