stichii

<button type="submit" class="btn btn-default"><span>Submit</span></button>

.btn > span{
  position: relative; top: 0; left: 0;
}

<div class="row">
    <?php query_posts('cat=2&orderby=date&order=DESC&posts_per_page=3'); ?>

    <?php if(have_posts()): $i = 0; while(have_posts()): the_post(); ?>
        <div class="col-md-4 col-sm-6 <?php echo ($i % 3 == 0) ? 'hidden-sm' : ' '; ?>">
            <div class="content_post">
                <div id="post-<?php the_ID(); ?>" <?php post_class(); ?>>
                    <?php get_template_part( 'content', get_post_format() ); ?>
                </div>
            </div>
        </div>
    <?php $i++; endwhile; endif; ?>
</div>

<?php wp_reset_postdata(); ?>