Child theme for Options Page UI demo (https://www.youtube.com/watch?v=0As393DZyZs)

functions.php

<?php
/**
 * This file adds functions to the child WordPress theme.
 */

/**
 * Check for Notification Bar, and display it.
 */
function demo_acf_output_notification() {
	$has_notice = get_field( 'notification_bar', 'options' );

	if ( ! $has_notice || ! $has_notice['notification_onoff'] ) {
		return;
	}
	?>

	<div class="notification-bar">
		<div class="notification-bar__inner">
			<p>
				<?php echo wp_kses_post( $has_notice['notification_message'] ); ?>
			</p>
		</div>
	</div>
	<?php
}
// Notification to be placed after opening body tag.
add_action( 'wp_body_open', 'demo_acf_output_notification' );

style.css

/*
Theme Name:   ACF Child
Description:  A WordPress Child Theme
Author:       ACF
Template:     frost
License:      GNU General Public License v2 or later
License URI:  http://www.gnu.org/licenses/gpl-2.0.html
*/