Lightbox2 in Post Gallery plugin view

gallery.php

<style type="text/css">
.post-gallery a {position: relative;}
.post-gallery .is-video:before {
    content: "\f236"; position: absolute; font-family: Dashicons; font-size: 50px;
    color: #fff; top: calc(50% - 30px); left: calc(50% - 30px); text-shadow: 0 0 4px #000;
}
</style>
<div class="post-gallery">
    <?php foreach ( $post->gallery as $attachment ) : ?>
        <a href="<?php echo $attachment->is_video ? $attachment->video_url : $attachment->url ?>"
            <?php if ( $attachment->is_video ) : ?>
                class="is-video"
            <?php else : ?>
                data-lightbox="post-gallery-<?php echo $post->ID ?>"
                <?php if ( $attachment->caption ) : ?>
                    data-title="<?php echo $attachment->caption ?>"
                <?php endif ?>
            <?php endif ?>
        >
            <img src="<?php echo $attachment->thumb_url ?>"
                alt="<?php echo $attachment->alt ?>"
            />
        </a>
    <?php endforeach ?>
</div>