How to attach custom CSS to a Views output?
You will need hook_views_pre_render().

And here is an example:

/**
 * Implements hook_views_pre_render().
 */
function base_views_pre_render(ViewExecutable $view) {
  if($view-&gt;id() == 'this_is_my_view_with_no_css' &amp;&amp; $view-&gt;current_display == 'page_1') {
    $view-&gt;element['#attached']['library'][] = 'base/test';
  }
}