Describe the bug

On IE11, Navigation block submenu dropdowns don't open when the parent block is hovered or focused. The focus behaviour is relying on :focus-within, which isn't supported on IE, but I'm not sure why the hover functionality also doesn't work.

Because the styles for hiding the dropdown use visibility: hidden there's also a risk it won't be accessible on screen readers if using IE.

To reproduce
Steps to reproduce the behavior:

1. Create a new post.
2. Add navigation block and create a submenu for one of the items.
3. On IE, try to access the submenu by hovering or focusing on the parent item.
4. Verify that submenu remains hidden.

Expected behavior

Expected submenu to be accessible on IE.

Screenshots