diff -u b/core/profiles/demo_umami/themes/umami/js/components/navigation/menu-main/menu-main.es6.js b/core/profiles/demo_umami/themes/umami/js/components/navigation/menu-main/menu-main.es6.js
--- b/core/profiles/demo_umami/themes/umami/js/components/navigation/menu-main/menu-main.es6.js
+++ b/core/profiles/demo_umami/themes/umami/js/components/navigation/menu-main/menu-main.es6.js
@@ -9,21 +9,24 @@
   );
   const menu = document.querySelector('[data-drupal-selector="menu-main"]');
 
-  menu.classList.toggle('menu-main--collapsed');
+  menu.classList.add('menu-main--collapsed');
   toggler.setAttribute('aria-expanded', 'false');
   toggler.setAttribute('aria-controls', menu.getAttribute('id'));
 
   function toggleMenu() {
     const expanded = toggler.getAttribute('aria-expanded');
 
+    // We want to avoid showing a collapse on page load, so don't enable the CSS
+    // transitions until the button is actually pressed for the first time. This
+    // class should remain in place during subsequent presses.
     menu.classList.add('menu-main--transition');
-    menu.classList.toggle('menu-main--collapsed');
-    toggler.classList.toggle('menu-main-toggle--active');
 
     if (expanded === 'false') {
       toggler.setAttribute('aria-expanded', 'true');
+      menu.classList.remove('menu-main--collapsed');
     } else {
       toggler.setAttribute('aria-expanded', 'false');
+      menu.classList.add('menu-main--collapsed');
     }
   }
 
diff -u b/core/profiles/demo_umami/themes/umami/js/components/navigation/menu-main/menu-main.js b/core/profiles/demo_umami/themes/umami/js/components/navigation/menu-main/menu-main.js
--- b/core/profiles/demo_umami/themes/umami/js/components/navigation/menu-main/menu-main.js
+++ b/core/profiles/demo_umami/themes/umami/js/components/navigation/menu-main/menu-main.js
@@ -9,7 +9,7 @@
   var toggler = document.querySelector('[data-drupal-selector="menu-main-toggle"]');
   var menu = document.querySelector('[data-drupal-selector="menu-main"]');
 
-  menu.classList.toggle('menu-main--collapsed');
+  menu.classList.add('menu-main--collapsed');
   toggler.setAttribute('aria-expanded', 'false');
   toggler.setAttribute('aria-controls', menu.getAttribute('id'));
 
@@ -17,13 +17,13 @@
     var expanded = toggler.getAttribute('aria-expanded');
 
     menu.classList.add('menu-main--transition');
-    menu.classList.toggle('menu-main--collapsed');
-    toggler.classList.toggle('menu-main-toggle--active');
 
     if (expanded === 'false') {
       toggler.setAttribute('aria-expanded', 'true');
+      menu.classList.remove('menu-main--collapsed');
     } else {
       toggler.setAttribute('aria-expanded', 'false');
+      menu.classList.add('menu-main--collapsed');
     }
   }