Create link with attributes in Drupal 8

url.php

<?php
$link_url = Url::fromRoute('node.add', array('node_type' => $content_type));
$link_url->setOptions(array(
 'attributes' => array('class' => 'button button-action button--primary button--small'),
 'query' => \Drupal::destination()->getAsArray(),
));
$link_text = t('Add !content_type content', array('!content_type' => ucfirst($content_type)));
// Build link
$link = \Drupal::l($link_text, $link_url);
?>