How to apply a CSS style to fuzzy or untranslated strings?

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I'm working on a manual that has translated variants via .po/.mo files. I'd like to apply a specific style to the generated HTML if translated strings are either marked as fuzzy (needs work) or are untranslated.
 
I found some documentation on how to do this on classic Sphinx theme, but I don't understand how to apply it to Furo. The article I found said to do something like this in the layout.html:

{% extends "!layout.html" %}

{% block content %}
  {% for item in doc %}
    {% if item.fuzzy %}
      <div class="fuzzy">{{ item.msgstr }}</div>
    {% else if not item.msgstr %}
      <div class="untranslated">{{ item.msgid }}</div>
    {% else %}
      {{ item.msgstr }}
    {% endif %}
  {% endfor %}
{% endblock %}

But I have no idea where to apply this to Furo. Any suggestions are most welcome.