WordPress/wp-content/themes/twentyfifteen/search.php

<?php
/**
 * The template for displaying search results pages.
 *
 * @package WordPress
 * @subpackage Twenty_Fifteen
 * @since Twenty Fifteen 1.0
 */

get_header(); ?>

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

		<?php if ( have_posts() ) : ?>

			<header class="page-header">
				<h1 class="page-title">
				<?php
				/* translators: %s: search query */
				printf( __( 'Search Results for: %s', 'twentyfifteen' ), get_search_query() );
				?>
				</h1>
			</header><!-- .page-header -->

			<?php
			// Start the loop.
			while ( have_posts() ) :
				the_post();
				?>

				<?php
				/*
				 * Run the loop for the search to output the results.
				 * If you want to overload this in a child theme then include a file
				 * called content-search.php and that will be used instead.
				 */
				get_template_part( 'content', 'search' );

				// End the loop.
			endwhile;

			// Previous/next page navigation.
			the_posts_pagination(
				array(
					'prev_text'          => __( 'Previous page', 'twentyfifteen' ),
					'next_text'          => __( 'Next page', 'twentyfifteen' ),
					'before_page_number' => '<span class="meta-nav screen-reader-text">' . __( 'Page', 'twentyfifteen' ) . ' </span>',
				)
			);

			// If no content, include the "No posts found" template.
		else :
			get_template_part( 'content', 'none' );

		endif;
		?>

		</main><!-- .site-main -->
	</section><!-- .content-area -->

<?php get_footer(); ?>