Index: src/wp-content/themes/twentyseventeen/assets/js/navigation.js
===================================================================
--- src/wp-content/themes/twentyseventeen/assets/js/navigation.js	(revision 39433)
+++ src/wp-content/themes/twentyseventeen/assets/js/navigation.js	(working copy)
@@ -17,8 +17,13 @@
 
 		container.find( '.menu-item-has-children > a, .page_item_has_children > a' ).after( dropdownToggle );
 
-		// Toggle buttons and submenu items with active children menu items.
-		container.find( '.current-menu-ancestor > button' ).addClass( 'toggled-on' );
+		// Set the active submenu dropdown toggle button initial state.
+		container.find( '.current-menu-ancestor > button' )
+			.addClass( 'toggled-on' )
+			.attr( 'aria-expanded', 'true' )
+			.find( '.screen-reader-text' )
+			.text( twentyseventeenScreenReaderText.collapse );
+		// Set the active submenu initial state.
 		container.find( '.current-menu-ancestor > .sub-menu' ).addClass( 'toggled-on' );
 
 		container.find( '.dropdown-toggle' ).click( function( e ) {
@@ -50,15 +55,13 @@
 			return;
 		}
 
-		// Add an initial values for the attribute.
-		menuToggle.add( siteNavigation ).attr( 'aria-expanded', 'false' );
+		// Add an initial value for the attribute.
+		menuToggle.attr( 'aria-expanded', 'false' );
 
 		menuToggle.on( 'click.twentyseventeen', function() {
-			$( siteNavContain ).toggleClass( 'toggled-on' );
+			siteNavContain.toggleClass( 'toggled-on' );
 
-			$( this )
-				.add( siteNavigation )
-				.attr( 'aria-expanded', $( this ).add( siteNavigation ).attr( 'aria-expanded' ) === 'false' ? 'true' : 'false' );
+			$( this ).attr( 'aria-expanded', siteNavContain.hasClass( 'toggled-on' ) );
 		});
 	})();
 
@@ -103,32 +106,4 @@
 			$( this ).parents( '.menu-item, .page_item' ).toggleClass( 'focus' );
 		});
 	})();
-
-	// Add the default ARIA attributes for the menu toggle and the navigations.
-	function onResizeARIA() {
-		if ( 'block' === $( '.menu-toggle' ).css( 'display' ) ) {
-
-			if ( menuToggle.hasClass( 'toggled-on' ) ) {
-				menuToggle.attr( 'aria-expanded', 'true' );
-			} else {
-				menuToggle.attr( 'aria-expanded', 'false' );
-			}
-
-			if ( siteNavigation.closest( '.main-navigation' ).hasClass( 'toggled-on' ) ) {
-				siteNavigation.attr( 'aria-expanded', 'true' );
-			} else {
-				siteNavigation.attr( 'aria-expanded', 'false' );
-			}
-		} else {
-			menuToggle.removeAttr( 'aria-expanded' );
-			siteNavigation.removeAttr( 'aria-expanded' );
-			menuToggle.removeAttr( 'aria-controls' );
-		}
-	}
-
-	$( document ).ready( function() {
-		$( window ).on( 'load.twentyseventeen', onResizeARIA );
-		$( window ).on( 'resize.twentyseventeen', onResizeARIA );
-	});
-
 })( jQuery );