accounts/common/mail/layouts/text.php

<?php
/**
 * @var $this \yii\web\View view component instance
 * @var $message \yii\mail\MessageInterface the message being composed
 * @var $content string main view render result
 */

?>
<?php $this->beginPage() ?>
<?php $this->beginBody() ?>
<?= $content ?>
<?php $this->endBody() ?>
<?php $this->endPage() ?>