edit lib/content.php

Post Grid

<div class="col-md-3 post-grid">
  <article <?php post_class(); ?>>
    <header>
      <a href="<?php the_permalink(); ?>">
        <?php if (has_post_thumbnail()): ?>
        <?php the_post_thumbnail('', array('class' => 'center img-responsive')); ?>
        <?php else : ?>
          <img class="center img-responsive" src="<?php echo get_template_directory_uri(); ?>/assets/img/placeholder.jpg">
        <?php endif; ?>
      </a>
      <h2 class="entry-title"><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h2>
      <?php get_template_part('templates/entry-meta'); ?>
    </header>
    <div class="entry-summary">
      <?php the_excerpt(); ?>
    </div>
  </article>
</div>