Add class to the body/html when on error page

How to add class to the body when user is on particular page? In my case this is “error” page (404/403 etc.)

I should add that I want to do it for .twig page, not .md page.

Solved it! In case someone is looking for same solution:

In my base.html.twig I have:

{% block body %}
{% endblock %}

In my error page error.html.twig I defined a class that will be added to the body everytime browser display error page:

{% block body %}
<body class="error-page">
{% endblock %}

And then I target in CSS:

body.error-page { 
 // your css