understrap/loop-templates/content-verticalpage.php

<?php
/**
 * The template used for displaying page content in a vertical layout
 * The template modifies Article's ID by using post's slug to lower case as anchor point.
 * @package understrap
 */
?>

<?php global $post ?>

<article id="<?php echo strtolower( $post->post_title ); ?>" <?php post_class(); ?>>

  <header class="entry-header">

    <?php the_title( '<h2 class="entry-title">', '</h2>' ); ?>

  </header><!-- .entry-header -->

  <?php echo get_the_post_thumbnail( $post->ID, 'large' ); ?>

  <div class="entry-content">

    <?php the_content(); ?>

    <?php
    wp_link_pages( array(
      'before' => '<div class="page-links">' . __( 'Pages:', 'understrap' ),
      'after'  => '</div>',
    ) );
    ?>

  </div><!-- .entry-content -->

  <footer class="entry-footer">

    <?php edit_post_link( __( 'Edit', 'understrap' ), '<span class="edit-link">', '</span>' ); ?>

  </footer><!-- .entry-footer -->

</article><!-- #post-## -->