Mark first day of multiday events (month view)

<?php
/**
 * Month Single Event
 *
 * This has been customized to add an extra CSS class .first_day_marker to multiday
 * events displaying on the *first* day for which they run.
 */

if ( !defined('ABSPATH') ) { die('-1'); } ?>

<?php

global $post;
$day = tribe_events_get_current_month_day();
$event_id = "{$post->ID}-{$day['daynum']}";
$start = tribe_get_start_date( $post, FALSE, 'U' );
$end = tribe_get_end_date( $post, FALSE, 'U' );

$first_day = ( $day['date'] === date('Y-m-d', $start) );
$multi_day = tribe_event_is_multiday( get_the_ID() );

?>

<div id="tribe-events-event-<?php echo $event_id ?>" class="<?php tribe_events_event_classes() ?>">
    <?php
    // If this is the first day of a multiday event, add some kind of marker
    // (you could alternatively add an extra CSS class)
    if ( $first_day && $multi_day ) echo ' <strong> Class begins </strong> ';
    ?>
    <h3 class="tribe-events-month-event-title summary"><a href="<?php tribe_event_link( $post ); ?>" class="url"><?php the_title() ?></a></h3>
    <div id="tribe-events-tooltip-<?php echo $event_id; ?>" class="tribe-events-tooltip">
        <h4 class="summary"><?php the_title() ?></h4>
        <div class="tribe-events-event-body">

            <?php echo tribe_events_event_schedule_details() ?>

            <?php if (has_post_thumbnail() ) : ?>
                <div class="tribe-events-event-thumb"><?php echo the_post_thumbnail(array(90,90));?></div>
            <?php endif; ?>

            <p class="entry-summary description">
                <?php echo get_the_excerpt() ?>
            </p><!-- .entry-summary -->

        </div><!-- .tribe-events-event-body -->
        <span class="tribe-events-arrow"></span>
    </div><!-- .tribe-events-tooltip -->
</div><!-- #tribe-events-event-# -->