Не определенная функция get_header

    <?php
    /**
     * The main template file
     *
     * This is the most generic template file in a WordPress theme
     * and one of the two required files for a theme (the other being style.css).
     * It is used to display a page when nothing more specific matches a query.
     * E.g., it puts together the home page when no home.php file exists.
     *
     * @link https://developer.wordpress.org/themes/basics/template-hierarchy/
     *
     * @package WorldElectronics
     */

    get_header();
    ?>

        <main id="primary" class="site-main">

            <?php
            if ( have_posts() ) :

                if ( is_home() && ! is_front_page() ) :
                    ?>
                    <header>
                        <h1 class="page-title screen-reader-text"><?php single_post_title(); ?></h1>
                    </header>
                    <?php
                endif;

                /* Start the Loop */
                while ( have_posts() ) :
                    the_post();

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

                endwhile;

                the_posts_navigation();

            else :

                get_template_part( 'template-parts/content', 'none' );

            endif;
            ?>

        </main><!-- #main -->

    <?php
    get_sidebar();
    get_footer();