Steps to reproduce:
- Go to an article with many references and edit it with VisualEditor, e.g. https://en.wikipedia.org/w/index.php?title=Brenna_Lovera&veaction=edit
- Click "Cite" and "Re-use" to insert a new reference that reuses an existing one.
- While the text cursor is in the search field, keep pressing the cursor up/down keys. Notice how the list below the input field starts scrolling at some point as if we are somehow navigating it. But there is no visual indication for what's actually going on.
- We can even press enter to insert one of the reference. We just can't see which one is selected.
It's really only a line of CSS that's missing. I suspect this once worked but got lost with some OOUI update.