Update spacer to match upstream rank

packages/application-extension/src/index.ts

@@ -341,7 +341,9 @@ const shell: JupyterFrontEndPlugin<IRetroShell> = {
 };
 
 /**
- * A plugin to provide a spacer at rank 10000 for flex panels
+ * A plugin to provide a spacer at rank 900 for flex panels
+ * TODO: reuse upstream @jupyterlab/application-extension:top-spacer plugin when fixed
+ * in https://github.com/jupyterlab/jupyterlab/pull/11900
  */
 const spacer: JupyterFrontEndPlugin<void> = {
   id: '@retrolab/application-extension:spacer',
@@ -350,12 +352,12 @@ const spacer: JupyterFrontEndPlugin<void> = {
     const top = new Widget();
     top.id = DOMUtils.createDomID();
     top.addClass('jp-RetroSpacer');
-    app.shell.add(top, 'top', { rank: 10000 });
+    app.shell.add(top, 'top', { rank: 900 });
 
     const menu = new Widget();
     menu.id = DOMUtils.createDomID();
     menu.addClass('jp-RetroSpacer');
-    app.shell.add(menu, 'menu', { rank: 10000 });
+    app.shell.add(menu, 'menu', { rank: 900 });
   }
 };