Source: templates/emails/teacher-completed-lesson.php

<?php
/**
 * Teacher completed course email
 *
 * @author  Automattic
 * @package Sensei/Templates/Emails/HTML
 * @version 2.0.0
 */

// phpcs:disable VariableAnalysis.CodeAnalysis.VariableAnalysis.UndefinedVariable

if ( ! defined( 'ABSPATH' ) ) {
	exit;
} // Exit if accessed directly ?>

<?php

// Get data for email content
global $sensei_email_data;
extract( $sensei_email_data );

// For gmail compatibility, including CSS styles in head/body are stripped out therefore styles need to be inline. These variables contain rules which are added to the template inline. !important; is a gmail hack to prevent styles being stripped if it doesn't like something.
$small = 'text-align: center !important;';

$large = 'text-align: center !important;font-size: 350% !important;line-height: 100% !important;';

?>

<?php
/**
 * Action hook before email content.
 *
 * @hook sensei_before_email_content
 *
 * @param {string} $template Template name.
 */
do_action( 'sensei_before_email_content', $template );
?>

<p style="<?php echo esc_attr( $small ); ?>"><?php esc_html_e( 'Your student', 'sensei-lms' ); ?></p>

<h2 style="<?php echo esc_attr( $large ); ?>"><?php echo esc_html( $learner_name ); ?></h2>

<p style="<?php echo esc_attr( $small ); ?>"><?php echo esc_html__( 'has completed the lesson', 'sensei-lms' ); ?></p>

<h2 style="<?php echo esc_attr( $large ); ?>"><?php echo esc_html( get_the_title( $lesson_id ) ); ?></h2>

<hr/>

<p style="<?php echo esc_attr( $small ); ?>">
<?php
// translators: Placeholders are an opening and closing <a> tag linking to the lesson's learners page.
printf( esc_html__( 'Manage this lesson\'s students %1$shere%2$s.', 'sensei-lms' ), '<a href="' . esc_url( admin_url( 'admin.php?page=sensei_learners&view=learners&lesson_id=' . $lesson_id ) ) . '">', '</a>' );
?>
</p>

<?php
/**
 * Action hook after email content.
 *
 * @hook sensei_after_email_content
 *
 * @param {string} $template Template name.
 */
do_action( 'sensei_after_email_content', $template );
?>