Index: src/wp-admin/my-sites.php
===================================================================
--- src/wp-admin/my-sites.php	(revision 55416)
+++ src/wp-admin/my-sites.php	(working copy)
@@ -56,7 +56,7 @@
 require_once ABSPATH . 'wp-admin/admin-header.php';
 
 if ( $updated ) { ?>
-	<div id="message" class="updated notice is-dismissible"><p><strong><?php _e( 'Settings saved.' ); ?></strong></p></div>
+	<div id="message" class="notice notice-success is-dismissible"><p><strong><?php _e( 'Settings saved.' ); ?></strong></p></div>
 <?php } ?>
 
 <div class="wrap">
@@ -74,9 +74,9 @@
 }
 
 if ( empty( $blogs ) ) :
-	echo '<p>';
-	_e( 'You must be a member of at least one site to use this page.' );
-	echo '</p>';
+	?>
+	<div class="notice notice-error is-dismissible"><p><strong><?php _e( 'You must be a member of at least one site to use this page.' ); ?></strong></p></div>
+	<?php
 else :
 	?>
 
Index: src/wp-admin/network/settings.php
===================================================================
--- src/wp-admin/network/settings.php	(revision 55416)
+++ src/wp-admin/network/settings.php	(working copy)
@@ -138,7 +138,7 @@
 require_once ABSPATH . 'wp-admin/admin-header.php';
 
 if ( isset( $_GET['updated'] ) ) {
-	?><div id="message" class="updated notice is-dismissible"><p><?php _e( 'Settings saved.' ); ?></p></div>
+	?><div id="message" class="notice notice-success is-dismissible"><p><?php _e( 'Settings saved.' ); ?></p></div>
 	<?php
 }
 ?>
@@ -167,7 +167,7 @@
 					$new_admin_email = get_site_option( 'new_admin_email' );
 					if ( $new_admin_email && get_site_option( 'admin_email' ) !== $new_admin_email ) :
 						?>
-						<div class="updated inline">
+						<div class="notice notice-warning is-dismissible inline">
 						<p>
 						<?php
 							printf(
Index: src/wp-admin/network/site-info.php
===================================================================
--- src/wp-admin/network/site-info.php	(revision 55416)
+++ src/wp-admin/network/site-info.php	(working copy)
@@ -147,7 +147,7 @@
 
 if ( ! empty( $messages ) ) {
 	foreach ( $messages as $msg ) {
-		echo '<div id="message" class="updated notice is-dismissible"><p>' . $msg . '</p></div>';
+		echo '<div id="message" class="notice notice-success is-dismissible"><p>' . $msg . '</p></div>';
 	}
 }
 ?>
Index: src/wp-admin/network/site-new.php
===================================================================
--- src/wp-admin/network/site-new.php	(revision 55416)
+++ src/wp-admin/network/site-new.php	(working copy)
@@ -189,7 +189,7 @@
 <?php
 if ( ! empty( $messages ) ) {
 	foreach ( $messages as $msg ) {
-		echo '<div id="message" class="updated notice is-dismissible"><p>' . $msg . '</p></div>';
+		echo '<div id="message" class="notice notice-success is-dismissible"><p>' . $msg . '</p></div>';
 	}
 }
 ?>
Index: src/wp-admin/network/site-settings.php
===================================================================
--- src/wp-admin/network/site-settings.php	(revision 55416)
+++ src/wp-admin/network/site-settings.php	(working copy)
@@ -105,7 +105,7 @@
 
 if ( ! empty( $messages ) ) {
 	foreach ( $messages as $msg ) {
-		echo '<div id="message" class="updated notice is-dismissible"><p>' . $msg . '</p></div>';
+		echo '<div id="message" class="notice notice-success is-dismissible"><p>' . $msg . '</p></div>';
 	}
 }
 ?>
Index: src/wp-admin/network/site-themes.php
===================================================================
--- src/wp-admin/network/site-themes.php	(revision 55416)
+++ src/wp-admin/network/site-themes.php	(working copy)
@@ -195,7 +195,7 @@
 		/* translators: %s: Number of themes. */
 		$message = _n( '%s theme enabled.', '%s themes enabled.', $enabled );
 	}
-	echo '<div id="message" class="updated notice is-dismissible"><p>' . sprintf( $message, number_format_i18n( $enabled ) ) . '</p></div>';
+	echo '<div id="message" class="notice notice-success is-dismissible"><p>' . sprintf( $message, number_format_i18n( $enabled ) ) . '</p></div>';
 } elseif ( isset( $_GET['disabled'] ) ) {
 	$disabled = absint( $_GET['disabled'] );
 	if ( 1 === $disabled ) {
@@ -204,9 +204,9 @@
 		/* translators: %s: Number of themes. */
 		$message = _n( '%s theme disabled.', '%s themes disabled.', $disabled );
 	}
-	echo '<div id="message" class="updated notice is-dismissible"><p>' . sprintf( $message, number_format_i18n( $disabled ) ) . '</p></div>';
+	echo '<div id="message" class="notice notice-success is-dismissible"><p>' . sprintf( $message, number_format_i18n( $disabled ) ) . '</p></div>';
 } elseif ( isset( $_GET['error'] ) && 'none' === $_GET['error'] ) {
-	echo '<div id="message" class="error notice is-dismissible"><p>' . __( 'No theme selected.' ) . '</p></div>';
+	echo '<div id="message" class="notice notice-error is-dismissible"><p>' . __( 'No theme selected.' ) . '</p></div>';
 }
 ?>
 
Index: src/wp-admin/network/site-users.php
===================================================================
--- src/wp-admin/network/site-users.php	(revision 55416)
+++ src/wp-admin/network/site-users.php	(working copy)
@@ -235,37 +235,37 @@
 if ( isset( $_GET['update'] ) ) :
 	switch ( $_GET['update'] ) {
 		case 'adduser':
-			echo '<div id="message" class="updated notice is-dismissible"><p>' . __( 'User added.' ) . '</p></div>';
+			echo '<div id="message" class="notice notice-success is-dismissible"><p>' . __( 'User added.' ) . '</p></div>';
 			break;
 		case 'err_add_member':
-			echo '<div id="message" class="error notice is-dismissible"><p>' . __( 'User is already a member of this site.' ) . '</p></div>';
+			echo '<div id="message" class="notice notice-error  is-dismissible"><p>' . __( 'User is already a member of this site.' ) . '</p></div>';
 			break;
 		case 'err_add_fail':
-			echo '<div id="message" class="error notice is-dismissible"><p>' . __( 'User could not be added to this site.' ) . '</p></div>';
+			echo '<div id="message" class="notice notice-error is-dismissible"><p>' . __( 'User could not be added to this site.' ) . '</p></div>';
 			break;
 		case 'err_add_notfound':
-			echo '<div id="message" class="error notice is-dismissible"><p>' . __( 'Enter the username of an existing user.' ) . '</p></div>';
+			echo '<div id="message" class="notice notice-error is-dismissible"><p>' . __( 'Enter the username of an existing user.' ) . '</p></div>';
 			break;
 		case 'promote':
-			echo '<div id="message" class="updated notice is-dismissible"><p>' . __( 'Changed roles.' ) . '</p></div>';
+			echo '<div id="message" class="notice notice-success is-dismissible"><p>' . __( 'Changed roles.' ) . '</p></div>';
 			break;
 		case 'err_promote':
-			echo '<div id="message" class="error notice is-dismissible"><p>' . __( 'Select a user to change role.' ) . '</p></div>';
+			echo '<div id="message" class="notice notice-error is-dismissible"><p>' . __( 'Select a user to change role.' ) . '</p></div>';
 			break;
 		case 'remove':
-			echo '<div id="message" class="updated notice is-dismissible"><p>' . __( 'User removed from this site.' ) . '</p></div>';
+			echo '<div id="message" class="notice notice-success is-dismissible"><p>' . __( 'User removed from this site.' ) . '</p></div>';
 			break;
 		case 'err_remove':
-			echo '<div id="message" class="error notice is-dismissible"><p>' . __( 'Select a user to remove.' ) . '</p></div>';
+			echo '<div id="message" class="notice notice-error is-dismissible"><p>' . __( 'Select a user to remove.' ) . '</p></div>';
 			break;
 		case 'newuser':
-			echo '<div id="message" class="updated notice is-dismissible"><p>' . __( 'User created.' ) . '</p></div>';
+			echo '<div id="message" class="notice notice-success is-dismissible"><p>' . __( 'User created.' ) . '</p></div>';
 			break;
 		case 'err_new':
-			echo '<div id="message" class="error notice is-dismissible"><p>' . __( 'Enter the username and email.' ) . '</p></div>';
+			echo '<div id="message" class="notice notice-error is-dismissible"><p>' . __( 'Enter the username and email.' ) . '</p></div>';
 			break;
 		case 'err_new_dup':
-			echo '<div id="message" class="error notice is-dismissible"><p>' . __( 'Duplicated username or email address.' ) . '</p></div>';
+			echo '<div id="message" class="notice notice-error is-dismissible"><p>' . __( 'Duplicated username or email address.' ) . '</p></div>';
 			break;
 	}
 endif;
Index: src/wp-admin/network/sites.php
===================================================================
--- src/wp-admin/network/sites.php	(revision 55416)
+++ src/wp-admin/network/sites.php	(working copy)
@@ -354,7 +354,7 @@
 	}
 
 	if ( ! empty( $msg ) ) {
-		$msg = '<div id="message" class="updated notice is-dismissible"><p>' . $msg . '</p></div>';
+		$msg = '<div id="message" class="notice notice-success is-dismissible"><p>' . $msg . '</p></div>';
 	}
 }
 
Index: src/wp-admin/network/themes.php
===================================================================
--- src/wp-admin/network/themes.php	(revision 55416)
+++ src/wp-admin/network/themes.php	(working copy)
@@ -375,7 +375,7 @@
 		/* translators: %s: Number of themes. */
 		$message = _n( '%s theme enabled.', '%s themes enabled.', $enabled );
 	}
-	echo '<div id="message" class="updated notice is-dismissible"><p>' . sprintf( $message, number_format_i18n( $enabled ) ) . '</p></div>';
+	echo '<div id="message" class="notice notice-updated is-dismissible"><p>' . sprintf( $message, number_format_i18n( $enabled ) ) . '</p></div>';
 } elseif ( isset( $_GET['disabled'] ) ) {
 	$disabled = absint( $_GET['disabled'] );
 	if ( 1 === $disabled ) {
@@ -384,7 +384,7 @@
 		/* translators: %s: Number of themes. */
 		$message = _n( '%s theme disabled.', '%s themes disabled.', $disabled );
 	}
-	echo '<div id="message" class="updated notice is-dismissible"><p>' . sprintf( $message, number_format_i18n( $disabled ) ) . '</p></div>';
+	echo '<div id="message" class="notice notice-updated is-dismissible"><p>' . sprintf( $message, number_format_i18n( $disabled ) ) . '</p></div>';
 } elseif ( isset( $_GET['deleted'] ) ) {
 	$deleted = absint( $_GET['deleted'] );
 	if ( 1 === $deleted ) {
@@ -393,7 +393,7 @@
 		/* translators: %s: Number of themes. */
 		$message = _n( '%s theme deleted.', '%s themes deleted.', $deleted );
 	}
-	echo '<div id="message" class="updated notice is-dismissible"><p>' . sprintf( $message, number_format_i18n( $deleted ) ) . '</p></div>';
+	echo '<div id="message" class="notice notice-success is-dismissible"><p>' . sprintf( $message, number_format_i18n( $deleted ) ) . '</p></div>';
 } elseif ( isset( $_GET['enabled-auto-update'] ) ) {
 	$enabled = absint( $_GET['enabled-auto-update'] );
 	if ( 1 === $enabled ) {
@@ -402,7 +402,7 @@
 		/* translators: %s: Number of themes. */
 		$message = _n( '%s theme will be auto-updated.', '%s themes will be auto-updated.', $enabled );
 	}
-	echo '<div id="message" class="updated notice is-dismissible"><p>' . sprintf( $message, number_format_i18n( $enabled ) ) . '</p></div>';
+	echo '<div id="message" class="notice notice-success is-dismissible"><p>' . sprintf( $message, number_format_i18n( $enabled ) ) . '</p></div>';
 } elseif ( isset( $_GET['disabled-auto-update'] ) ) {
 	$disabled = absint( $_GET['disabled-auto-update'] );
 	if ( 1 === $disabled ) {
@@ -411,11 +411,11 @@
 		/* translators: %s: Number of themes. */
 		$message = _n( '%s theme will no longer be auto-updated.', '%s themes will no longer be auto-updated.', $disabled );
 	}
-	echo '<div id="message" class="updated notice is-dismissible"><p>' . sprintf( $message, number_format_i18n( $disabled ) ) . '</p></div>';
+	echo '<div id="message" class="notice notice-success is-dismissible"><p>' . sprintf( $message, number_format_i18n( $disabled ) ) . '</p></div>';
 } elseif ( isset( $_GET['error'] ) && 'none' === $_GET['error'] ) {
-	echo '<div id="message" class="error notice is-dismissible"><p>' . __( 'No theme selected.' ) . '</p></div>';
+	echo '<div id="message" class="notice notice-error is-dismissible"><p>' . __( 'No theme selected.' ) . '</p></div>';
 } elseif ( isset( $_GET['error'] ) && 'main' === $_GET['error'] ) {
-	echo '<div class="error notice is-dismissible"><p>' . __( 'You cannot delete a theme while it is active on the main site.' ) . '</p></div>';
+	echo '<div id="message" class="notice notice-error is-dismissible"><p>' . __( 'You cannot delete a theme while it is active on the main site.' ) . '</p></div>';
 }
 
 ?>
Index: src/wp-admin/network/user-new.php
===================================================================
--- src/wp-admin/network/user-new.php	(revision 55416)
+++ src/wp-admin/network/user-new.php	(working copy)
@@ -77,8 +77,8 @@
 	}
 }
 
+$message = '';
 if ( isset( $_GET['update'] ) ) {
-	$messages = array();
 	if ( 'added' === $_GET['update'] ) {
 		$edit_link = '';
 		if ( isset( $_GET['user_id'] ) ) {
@@ -93,8 +93,6 @@
 		if ( $edit_link ) {
 			$message .= sprintf( ' <a href="%s">%s</a>', $edit_link, __( 'Edit user' ) );
 		}
-
-		$messages[] = $message;
 	}
 }
 
@@ -107,18 +105,16 @@
 <div class="wrap">
 <h1 id="add-new-user"><?php _e( 'Add New User' ); ?></h1>
 <?php
-if ( ! empty( $messages ) ) {
-	foreach ( $messages as $msg ) {
-		echo '<div id="message" class="updated notice is-dismissible"><p>' . $msg . '</p></div>';
-	}
+if ( '' !== $message ) {
+	echo '<div id="message" class="notice notice-success is-dismissible"><p>' . $message . '</p></div>';
 }
 
 if ( isset( $add_user_errors ) && is_wp_error( $add_user_errors ) ) {
 	?>
-	<div class="error">
+	<div id="message" class="notice notice-error is-dismissible">
 		<?php
-		foreach ( $add_user_errors->get_error_messages() as $message ) {
-			echo "<p>$message</p>";
+		foreach ( $add_user_errors->get_error_messages() as $error ) {
+			echo "<p>$error</p>";
 		}
 		?>
 	</div>
Index: src/wp-admin/network/users.php
===================================================================
--- src/wp-admin/network/users.php	(revision 55416)
+++ src/wp-admin/network/users.php	(working copy)
@@ -255,7 +255,7 @@
 
 if ( isset( $_REQUEST['updated'] ) && 'true' == $_REQUEST['updated'] && ! empty( $_REQUEST['action'] ) ) {
 	?>
-	<div id="message" class="updated notice is-dismissible"><p>
+	<div id="message" class="notice notice-success is-dismissible"><p>
 		<?php
 		switch ( $_REQUEST['action'] ) {
 			case 'delete':
