Drupal 8's theming layer is complemented by Twig, a component of the Symfony framework. Twig is a template language that uses a syntax similar to Django and Jinja templates. The previous version of Drupal used PHPTemplate that required frontend developers to have a rudimentary understanding of PHP.
In this recipe, we will override the Twig template to provide customizations for the e-mail form element. We will use the basic Twig syntax to add a new class and provide a default placeholder.
This recipe assumes that you have a custom theme created, such as the one you created in the first recipe. When you see
mytheme, use the machine name of the theme you created.
At the time of writing this module, the Classy theme ...