Make all user profile pictures round
In your file of your theme: "MYTHEME.theme"

Create hook_preprocess_image

/**
 * Implements hook_preprocess_image() to add classes to the search form.
 */
function MYTHEME_preprocess_image(&amp;$variables) {
  ksm ($variables);
    if ($variables['style_name'] == 'thumbnail') {
        $variables['attributes']['class'][] = 'image-rounded';
    }
}