Archives, Categories and Search to display in grid view

I would like the results of category, archives, and search to display in a grid view. I am using the Magazine-basic theme.

I have been searching and trying to understand what to edit to accomplish this. Nothing I have found makes this clear to me.

I have a wrapper div ready to go, if I knew where to place it. And I have css that works perfectly. The trouble I am having is in isolating the content for JUST those specified pages.

At first I inadvertently applied my new wrapper div to the content.php page and everything ended up in a grid of a specified width – even the single posts and pages.

So now I’m not sure I understand but I found this on my theme’s archive.php page:

<?php
			while ( have_posts() ) : the_post();
		    	global $mb_content_area;
		    	$mb_content_area = 'main';

		      	/* Include the post format-specific template for the content. If you want to
				 * this in a child theme then include a file called called content-___.php
				 * (where ___ is the post format) and that will be used instead.
				 */
		    	get_template_part( 'content', get_post_format() );

		    endwhile;

			mb_pagination();

		else :
			get_template_part( 'content', 'none' );
		endif;
		?>

If I understand the comments within that code correctly, I can use a child theme to affect the content only on the archive, search and category pages. But I’m not sure how to accomplish this.

Any help explaining the steps would be greatly appreciate. I am very familiar with css, but my php knowledge is only enough to make me dangerous to myself and others.

Did I mention I’m brand new to WP? 🙂

Any and all help kindly appreciated.