Untitled

// function.php

<?php

  function music_setup_theme(){
    add_theme_support('title-tag');
    add_theme_support('post-thumbnails');

    add_image_size( 'music-big', 1400, 800, true );
    add_image_size( 'music-quad', 600, 600, true );
    add_image_size( 'music-single', 800, 500, true );

    register_nav_menus( array(
      'header' => esc_html__('Header', 'music'),
    ));

  };

  add_action( 'after_setup_theme', 'music_setup_theme' );


 ?>

// index.php

<?php get_header(); ?>
<div id="main-content" class="main-content">
    <div id="content" class="content-area" role="main">
    </div><!-- #content -->
</div><!-- #main-content -->
<?php get_footer(); ?>


// header.php

<!DOCTYPE html>
<html <?php language_attributes(  ); ?> >
<head>
  <meta charset="">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <?php wp_head(); ?>
</head>
<body>
<header>
    <h1>Header</h1>
</header>


// footer.php


        <footer>

            <h2> Footer </h2>

        </footer>

        <?php wp_footer(); ?>

    </body>
</html>