Modify post page to display specific category

Website is MarioDidIt

The page template for this theme request all of my recent post (portfolio items)
however, I would like to just display one specific category.
For example, the “Graphic Design” category. (slug, “graphic-design”

Here is the current coding for the template.

<?php
get_header(); ?>

<?php
	if ( false === get_theme_mod( 'frontpage_header' ) ) {
		get_template_part( 'template-parts/home', 'tagline' );
	}else{
		get_template_part( 'template-parts/home', 'hero' );
} ?>

	<div id="primary" class="site-content">
		<main id="main" class="site-main" role="main">

                       <?php while ( have_posts() ) : the_post(); ?>

				<?php get_template_part( 'template-parts/page/content-home', 'mosaic' ); ?>

			<?php endwhile; // end of the loop. ?>

		</main><!-- #main -->
	</div><!-- #primary -->

<?php get_footer(); ?>

I tried modifying the “have post” line in that code but only seem to keep getting 503 errors.

Any help is greatly appreciated!
Thank you.