Fix admin sidebar on Mobile layout

app/javascript/flavours/glitch/packs/admin.js

@@ -1,6 +1,27 @@
 import 'packs/public-path';
+import loadPolyfills from 'flavours/glitch/util/load_polyfills';
 import ready from 'flavours/glitch/util/ready';
 
+function setupSidebar() {
+  const { delegate } = require('@rails/ujs');
+
+  delegate(document, '.sidebar__toggle__icon', 'click', () => {
+    const target = document.querySelector('.sidebar ul');
+
+    if (target.style.display === 'block') {
+      target.style.display = 'none';
+    } else {
+      target.style.display = 'block';
+    }
+  });
+}
+
+loadPolyfills()
+  .then(setupSidebar)
+  .catch(error => {
+    console.error(error);
+  });
+
 ready(() => {
   const React    = require('react');
   const ReactDOM = require('react-dom');