Search results in a grid

How can I make the results from the search show in grid view as a gallery using only the post’s main image? This is what I have done so far, but they go in a list, not a grid:

loop.php

<?php while (have_posts()) : the_post(); ?>
<div <?php post_class('post') ?>>
<a>"> <?php echo inkthemes_main_image(); ?> </a>
<h2 class="title" id="post-<?php the_ID(); ?>"><a>" rel="bookmark" title="<?php the_title_attribute(); ?>"><?php the_title(); ?></a></h2>
<?php endwhile; ?>

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