diff --git a/mu-plugins/blocks/local-navigation-bar/postcss/style.pcss b/mu-plugins/blocks/local-navigation-bar/postcss/style.pcss
index d49c96abc..19ff6bb7a 100644
--- a/mu-plugins/blocks/local-navigation-bar/postcss/style.pcss
+++ b/mu-plugins/blocks/local-navigation-bar/postcss/style.pcss
@@ -213,7 +213,8 @@
 		}
 	}
 
-	& .wp-block-navigation.is-collapsed {
+	& .wp-block-navigation.wporg-is-collapsed-nav,
+	& .wp-block-navigation.wporg-is-mobile-nav {
 
 		/* Remove padding from menu items with background color, which is used to color the modal background. */
 		&  ul.has-background {
diff --git a/mu-plugins/blocks/local-navigation-bar/src/view.js b/mu-plugins/blocks/local-navigation-bar/src/view.js
index db49c2db6..d0f3eefb9 100644
--- a/mu-plugins/blocks/local-navigation-bar/src/view.js
+++ b/mu-plugins/blocks/local-navigation-bar/src/view.js
@@ -42,17 +42,21 @@ function init() {
 		// CSS class to show the nav block with {"overlayMenu":"always"}
 		// added by `add_extra_navigation`.
 		const onResize = () => {
+			const navElement = container.querySelector( 'nav:not(.wporg-is-collapsed-nav)' );
+
 			// Bail early on small screens, the visible nav block is already mobile.
-			if ( window.innerWidth <= 600 ) {
+			if ( window.innerWidth < 600 ) {
 				container.classList.remove( 'wporg-show-collapsed-nav' );
+				navElement.classList.add( 'wporg-is-mobile-nav' );
 				return;
 			}
 
+			navElement.classList.remove( 'wporg-is-mobile-nav' );
+
 			// Fetch the navWidth from a data value which is set on page load,
 			// so that the uncollapsed visible menu's width is used.
 			let navWidth = container.dataset.navWidth;
 			if ( ! navWidth ) {
-				const navElement = container.querySelector( 'nav:not(.wporg-is-collapsed-nav)' );
 				const navGap = parseInt( window.getComputedStyle( navElement ).gap, 10 ) || 20;
 				// Get the nav width based on items, so that it stays
 				// consistent even if the menu wraps to a new line.