thumbnails in rows and columns

Hi, I am trying to get my thumbnail search results in rows and columns as opposed to the current layout which shows them one on top of the other.
RE: https://heritagecountrypottery.com/?s=slipware.
I believe this can be achieved with css but cannot work it out.
Please see my php and css below

PHP

<a href="<?php the_permalink(); ?>" title="<?php the_title();?>">
<?php if ( has_post_thumbnail() ): ?>
   <div class="search-thumbnail">
       <?php the_post_thumbnail(); ?>
   </div>
<?php endif; ?>
</a>

CSS

.search-thumbnail {
 width: 35%;
}