La revisión

https://make.wordpress.org/themes/handbook/review/required/theme-tags/

https://docs.emmet.io/cheat-sheet/

<?php body_class(); ?>

<?php get_header(); ?>
<?php get_footer(); ?>

<?php wp_head(); ?>
<?php wp_footer(); ?>

<?php
function load_scripts(){
    wp_enqueue_style('marks-theme', get_template_directory_uri().'/css/template.css', array(), '', 'all');
}
add_action('wp_enqueue_scripts', 'load_scripts');
?>


function load_scripts(){
    wp_enqueue_style('bootstrap', '//maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css', array(), '4.0.0', 'all');
    wp_enqueue_style('marks-theme', get_template_directory_uri().'/css/template.css', array(), '', 'all');

    wp_enqueue_script( 'popper-js', '//cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js', array(), '4.0.0', 'all' );
    wp_enqueue_script( 'bootstrap-js', '//maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js', array(), '4.0.0', 'all' );
    wp_enqueue_script( 'main-js', get_template_directory_uri().'/js/main.js', array(), '1.0', true );
}
add_action('wp_enqueue_scripts', 'load_scripts');



<meta name="viewport" content="width=device-width, initial-scale=1.0">