_content: made content activated by mouse dismissible using ESC key

https://screencast.googleplex.com/cast/NTcyNjIwNDA4MTQ3MTQ4OHwxOTQwNzQyNS04ZA

Change-Id: I4c804d97c7485cf75ea16260a6d4143cf0a70f69
Reviewed-on: https://go-review.googlesource.com/c/website/+/516196
Reviewed-by: Neelesh Bodas <neelesh@google.com>
Reviewed-by: Jamal Carvalho <jamal@golang.org>
Run-TryBot: Jamal Carvalho <jamal@golang.org>
Auto-Submit: Hyang-Ah Hana Kim <hyangah@gmail.com>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

_content/js/site.js

@@ -54,17 +54,20 @@ window.initFuncs = [];
         e.target.classList.add('forced-closed');
         e.target.classList.remove('forced-open');
       });
-    });
-
-    // ensure desktop submenus are closed when esc is pressed
-    const headerItems = document.querySelectorAll('.Header-menuItem');
-    headerItems.forEach(header => {
-      header.addEventListener('keyup', e => {
+      // ensure desktop submenus are closed when esc is pressed
+      const closeSubmenuOnEsc = e => {
         if (e.key === 'Escape') {
-          e.target.blur();
-          e.target.focus();
+          const forcedOpenItem = document.querySelector('.forced-open');
+          const target = e.currentTarget;
+          if (forcedOpenItem) {
+            forcedOpenItem.classList.remove('forced-open');
+            forcedOpenItem.blur();
+            forcedOpenItem.classList.add('forced-closed');
+          }
         }
-      });
+        e.target.focus();
+      };
+      document.addEventListener('keydown', closeSubmenuOnEsc);
     });
 
     // Mobile menu subnav menus