[2 column] posts, one category

Hi, i have some problems with my template for wp. I need 2 columns posts on one category, how fix empty space?

screenshot

.content{
width: 470px;
margin-left: 50px;
border: 1px solid blue;
float: left;
margin-bottom: 25px;
margin-top: 25px;
}

<?php
$args = array (
'category_name' => 'o nas',
'posts_per_page' => 999
 );
// the query
$the_query = new WP_Query( $args ); ?>
<?php if ( $the_query->have_posts() ) : ?>
  <?php while ( $the_query->have_posts() ) : $the_query->the_post(); ?>
    <div class="content">
<h3><?php the_title(); ?></h3>
<?php if ( has_post_thumbnail() ) { the_post_thumbnail( 'content_gallery_thumb', array('class' => 'content_gallery_thumb') ); } ?>
<?php the_content();?>
</div>
  <?php endwhile; ?>
  <?php wp_reset_postdata(); ?>
<?php else:  ?>
  <p><?php _e( 'Sorry, no posts matched your criteria.' ); ?></p>
<?php endif; ?>