Content preview blocks ability to click "Add block" link due to invisible menu items

Problem/Motivation

See 🐛 [random test failure] NavigationBlockUiTest::testNavigationBlockAdminUiPage failing Fixed

Steps to reproduce

Run the test without fix from linked issue

Proposed resolution

I'm not sure, everything has display grid but nothing is visible.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet