how can i show numbers on the thumbnail of post

How can I numbered my site like this site? please help me.. https://i.stack.imgur.com/T423E.jpg

my index.php
PHP Code:

<?php 

get_header(); ?> 

    <div id="primary" class="content-area">
        <main id="main" class="site-main" role="main"> 

        <?php if ( have_posts() ) : ?> 

            <?php /* Start the Loop */ ?>
            <?php while ( have_posts() ) : the_post(); ?> 

<?php 

$format = get_post_format();
$formats = get_theme_support( 'post-formats' );
$postclass = ''; 

if ( ! has_post_thumbnail() )
    $postclass = 'no-thumbnail';
?> 

<article id="post-<?php the_ID(); ?>" <?php post_class( $postclass ); ?>>
    <div class="entry-thumbnail">
        <a href="<?php the_permalink(); ?>" title="<?php echo the_title_attribute(); ?>">
            <?php if ( has_post_thumbnail() ) : ?>
                <?php the_post_thumbnail( 'pictorico-home' ); ?>
            <?php endif; ?>
        </a>
    </div>
    <header class="entry-header">
        <?php if ( 'post' == get_post_type() ) : ?>
        <div class="entry-meta">
            <?php pictorico_date(); ?>
        </div><!-- .entry-meta -->
        <?php if ( $format && in_array( $format, $formats[0] ) ): ?>
            <a class="entry-format" href="<?php echo esc_url( get_post_format_link( $format ) ); ?>" title="<?php echo esc_attr( sprintf( __( 'All %s posts', 'pictorico' ), get_post_format_string( $format ) ) ); ?>"><span class="screen-reader-text"><?php echo get_post_format_string( $format ); ?></span></a>
        <?php endif; ?>
        <?php endif; ?>
        <?php if ( 'link' == $format ) : ?>
            <?php the_title( '<h1 class="entry-title"><a href="' . esc_url( pictorico_get_link_url() ) . '" rel="bookmark">', '</a></h1>' ); ?>
        <?php else : ?>
            <?php the_title( '<h1 class="entry-title"><a href="' . esc_url( get_permalink() ) . '" rel="bookmark">', '</a></h1>' ); ?>
        <?php endif; ?>
    </header><!-- .entry-header --> 

    <footer class="entry-footer">
        <?php edit_post_link( __( 'Edit', 'pictorico' ), '<span class="edit-link">', '</span>' ); ?>
    </footer><!-- .entry-footer -->
</article><!-- #post-## --> 

            <?php endwhile; ?> 

            <?php pictorico_paging_nav(); ?> 

        <?php else : ?> 

            <?php get_template_part( 'content', 'none' ); ?> 

        <?php endif; ?> 

        </main><!-- #main -->
    </div><!-- #primary --> 

<?php get_footer(); ?>