How can I add a wrapper around my nodes? How can I wrap my nodes (output in teaser view) in a &lt;div&gt; element?

&lt;div class="region region-content"&gt;
  &lt;h1 class="js-quickedit-page-title page-header"&gt;My title&lt;/h1&gt;
  // &lt;div class="teasers"&gt; &lt;--- add this
    &lt;article&gt;...&lt;/article&gt;
    &lt;article&gt;...&lt;/article&gt;
    &lt;article&gt;...&lt;/article&gt;
    ...
  // &lt;/div&gt; &lt;--- add this
&lt;/div&gt;
Copy the corresponding twig template of your view into your module/theme and name it properly after the view's display, fe. views--{type, fe. unformatted}--my-view-id--my-block.html.twig.