How do I keep content's styles?
Content is not a variable of a field template. This is the reason kint(content) does not produce any output. The content of the field is in items:

  {% for item in items %}
    &lt;div{{ item.attributes }}&gt;{{ item.content }}&lt;/div&gt;
  {% endfor %}


Did you try twig debug to find the right template?

Debugging Twig templates

Edit: (Template in question was edited to node template)

This is no problem to add divs and classes to the node twig. Here is an example:

&lt;div class="container-outside-article"&gt;
  &lt;article{{ attributes.addClass('class-added-to-article') }}&gt;
    &lt;div class="container-inside-article"&gt;
      &lt;div{{ content_attributes }}&gt;
        {{ content }}
      &lt;/div&gt;
    &lt;/div&gt;
  &lt;/article&gt;
&lt;/div&gt;


I've added two container inside and outside the article tag and one class to the article tag itself.