Related Posts - Based on Category

<div class="related-posts-after-content">

    <?php
        $related_articles = array();
        $categories = get_the_category();

        if($categories) {
             $category_id = $categories[0]->term_id;

             if(count($categories) > 1 && class_exists('WPSEO_Primary_Term')) {
                    $primary_term = new WPSEO_Primary_Term('category', get_the_id());
                    $category_id  = $primary_term->get_primary_term();
             }

             $related_articles = get_posts(array(
                    'category'    => $category_id,
                    'exclude'     => $post->ID,
                    'numberposts' => 3,
                    'order'       => 'RAND',
                    'orderby'     => 'date',
                    'post_status' => 'published',
                    'post_type'   => 'post'
             ));
        }
    ?>

    <?php if($related_articles): ?>

        <h3>Like this blog post?  You'll love these...</h3>

     <section class="related-articles">
                <?php foreach($related_articles as $post): ?>
                     <?php setup_postdata($post); ?>
                     <article>
                            <?php if ( has_post_thumbnail() ) {
                                the_post_thumbnail(array(200,150));
                            } else { ?>
                            <img src="<?php bloginfo('template_directory'); ?>/images/default-image.jpg" alt="<?php the_title(); ?>" />
                            <?php } ?>
                            <br>
                            <h4><a href="<? the_permalink()?>"><?php the_title(); ?></a></h4>
                     </article>
                <?php endforeach; ?>
                <?php wp_reset_postdata(); ?>
         </section>
<?php endif; ?>

</div>

<style>
.related-posts-after-content {padding-top:20px;}

.related-posts-after-content article {
    display:inline-grid;
    width: 32%;
    text-align:center;
}

.related-posts-after-content article img {
    margin:auto;
}

.related-posts-after-content h3{
    font-family: Didot, serif;
    font-size: 30px;
    letter-spacing: 1px;
}
</style>