dlxsnippets/fullscreen-wp-admin.php

## fullscreen-wp-admin.php
<?php
/**
 * Plugin Name:       Fullscreen Admin Panel.
 * Plugin URI:        https://dlxplugins.com
 * Description:       A demo plugin to create a fullscreen admin panel.
 * Version:           1.0.0
 * Requires at least: 6.0
 * Requires PHP:      7.3
 * Author:            DLX Plugins
 * Author URI:        https://dlxplugins.com
 * License:           GPL v2 or later
 * License URI:       https://www.gnu.org/licenses/gpl-2.0.html
 *
 * @package DLXPlugins\FullscreenAdmin
 */

namespace DLXPlugins\FullscreenAdmin;

/**
 * Initialize the admin panel.
 */
add_action( 'admin_menu', __NAMESPACE__ . '\add_admin_menu' );

/**
 * Add the admin menu.
 */
function add_admin_menu() {
	add_dashboard_page(
		'',
		'',
		'manage_options',
		'my-admin-panel-slug',
		'',
		null
	);
}

// Add the admin page for full-screen.
add_action( 'current_screen', __NAMESPACE__ . '\maybe_output_admin_page', 10 );

/**
 * Output the dashboard admin page.
 */
function maybe_output_admin_page() {
	// Exit if not in admin.
	if ( ! is_admin() ) {
		return;
	}

	// Make sure we're on the right screen.
	$screen = get_current_screen();
	if ( 'my-admin-panel-slug' !== $screen->id ) {
		return;
	}
	get_admin_page_header();
	/**
	 * Begin body content.
	 */
	?>
	<main>
		Hello there.
	</main>
	<?php
	get_admin_page_footer();
	exit;
}

/**
 * Output landing page header.
 *
 * Credit: SliceWP Setup Wizard.
 */
function get_admin_page_header() {
	// Output header HTML.
	?>
	<!DOCTYPE html>
	<html <?php language_attributes(); ?>>
	<head>
		<meta name="viewport" content="width=device-width" />
		<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
		<title>My Admin Page Title</title>
		<?php
			wp_register_script(
				'my-plugin-admin-js',
				plugins_url( 'assets/js/admin.js', __FILE__ ),
				array(),
				'1.0.0',
				true
			);
			wp_register_style(
				'my-plugin-admin-css',
				plugins_url( 'assets/css/admin.css', __FILE__ ),
				array(),
				'1.0.0'
			);
			wp_print_styles( 'my-plugin-admin-css' );
			wp_print_scripts( 'my-plugin-admin-js' );
			?>
	</head>
	<body>
	<?php
}

/**
 * Output landing page footer.
 *
 * Credit: SliceWP Setup Wizard.
 */
function get_admin_page_footer() {
	// Output footer HTML.
	?>
	</body>
	</html>
	<?php
}
	<?php
	/**
	* Plugin Name: Fullscreen Admin Panel.
	* Plugin URI: https://dlxplugins.com
	* Description: A demo plugin to create a fullscreen admin panel.
	* Version: 1.0.0
	* Requires at least: 6.0
	* Requires PHP: 7.3
	* Author: DLX Plugins
	* Author URI: https://dlxplugins.com
	* License: GPL v2 or later
	* License URI: https://www.gnu.org/licenses/gpl-2.0.html
	*
	* @package DLXPlugins\FullscreenAdmin
	*/

	namespace DLXPlugins\FullscreenAdmin;

	/**
	* Initialize the admin panel.
	*/
	add_action( 'admin_menu', __NAMESPACE__ . '\add_admin_menu' );

	/**
	* Add the admin menu.
	*/
	function add_admin_menu() {
	add_dashboard_page(
	'',
	'',
	'manage_options',
	'my-admin-panel-slug',
	'',
	null
	);
	}

	// Add the admin page for full-screen.
	add_action( 'current_screen', __NAMESPACE__ . '\maybe_output_admin_page', 10 );

	/**
	* Output the dashboard admin page.
	*/
	function maybe_output_admin_page() {
	// Exit if not in admin.
	if ( ! is_admin() ) {
	return;
	}

	// Make sure we're on the right screen.
	$screen = get_current_screen();
	if ( 'my-admin-panel-slug' !== $screen->id ) {
	return;
	}
	get_admin_page_header();
	/**
	* Begin body content.
	*/
	?>
	<main>
	Hello there.
	</main>
	<?php
	get_admin_page_footer();
	exit;
	}

	/**
	* Output landing page header.
	*
	* Credit: SliceWP Setup Wizard.
	*/
	function get_admin_page_header() {
	// Output header HTML.
	?>
	<!DOCTYPE html>
	<html <?php language_attributes(); ?>>
	<head>
	<meta name="viewport" content="width=device-width" />
	<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
	<title>My Admin Page Title</title>
	<?php
	wp_register_script(
	'my-plugin-admin-js',
	plugins_url( 'assets/js/admin.js', __FILE__ ),
	array(),
	'1.0.0',
	true
	);
	wp_register_style(
	'my-plugin-admin-css',
	plugins_url( 'assets/css/admin.css', __FILE__ ),
	array(),
	'1.0.0'
	);
	wp_print_styles( 'my-plugin-admin-css' );
	wp_print_scripts( 'my-plugin-admin-js' );
	?>
	</head>
	<body>
	<?php
	}

	/**
	* Output landing page footer.
	*
	* Credit: SliceWP Setup Wizard.
	*/
	function get_admin_page_footer() {
	// Output footer HTML.
	?>
	</body>
	</html>
	<?php
	}