What’s wrong with this header.php file?

Try to find out what’s wrong with this header.php file. Here is the code of the header.php:

<?php
/**
 * The template for displaying the header
 *
 * @link https://developer.wordpress.org/themes/basics/template-files/#template-partials
 *
 * @package cliowp
 */

?>
<!DOCTYPE html>
<html <?php language_attributes(); ?>>

<head>
	<meta
		charset="<?php bloginfo( 'charset' ); ?>">
	<meta name="viewport" content="width=device-width, initial-scale=1">
</head>

<body <?php body_class(); ?>>

	<?php wp_body_open(); ?>

	<header>

		<div class="float-left">
			<p><a href="<?php echo esc_html( site_url() ); ?>"><?php echo esc_html( get_bloginfo( 'name' ) ); ?></a>
			</p>
		</div>

	</header>

Answer

You have to include the wp_head() function before the closing </head>

Example:

<head>
	<meta
		charset="<?php bloginfo( 'charset' ); ?>">
	<meta name="viewport" content="width=device-width, initial-scale=1">
	<?php wp_head(); ?>
</head>

Otherwise, the wp_enqueue_scripts() action hook will not work (neither for you nor for third-party plugins).