kdice-k/functions.php

## functions.php
<?php
function custom_theme_setup() {
  add_theme_support( 'menus' );
}
add_action( 'after_setup_theme', 'custom_theme_setup' );

## index.php
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <?php wp_head(); ?>
</head>
<body>
  <h1>テーマ機能 追加のテスト</h1>
  <?php wp_nav_menu(['menu' => 'main_nav']); ?>
  <?php wp_footer(); ?>
</body>
</html>

## style.css
@charset "utf-8";
/*
Theme Name: ざっくりテスト用
Theme URI: https://tmick.net
Description: シンプルテーマを作るテスト環境用
Version: 0.01
Author: D4isk
Author URI: https://tmick.net
*/

h1 {
  font-size: 24px;
}
	<?php
	function custom_theme_setup() {
	add_theme_support( 'menus' );
	}
	add_action( 'after_setup_theme', 'custom_theme_setup' );
	<!DOCTYPE html>
	<html lang="en">
	<head>
	<meta charset="UTF-8">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<title>Document</title>
	<?php wp_head(); ?>
	</head>
	<body>
	<h1>テーマ機能追加のテスト</h1>
	<?php wp_nav_menu(['menu' => 'main_nav']); ?>
	<?php wp_footer(); ?>
	</body>
	</html>
	@charset "utf-8";
	/*
	Theme Name: ざっくりテスト用
	Theme URI: https://tmick.net
	Description: シンプルテーマを作るテスト環境用
	Version: 0.01
	Author: D4isk
	Author URI: https://tmick.net
	*/

	h1 {
	font-size: 24px;
	}