[menu] Positioner is repositioned when navigating items

[aarongarciah]

Bug report

Current behavior

When the Popup part of the Menu is partly outside the viewport, if you navigate the options via ⬆️ ⬇️ keys, the positioner is repositioned. See attached video.

Kapture.2025-02-07.at.14.32.42.mp4

Expected behavior

The Popup should stay in the same place.

Reproducible example

https://codesandbox.io/p/sandbox/mns5dn?file=/src/App.tsx

Base UI version

1.0.0-alpha.6

[atomiks]

The interal scroll logic call .scrollIntoView({ block: 'nearest' }) causes this. Not sure if it matters given the CSS of the popup should have max-width: var(--available-width) which fixes both the layout overflow issue and this one.

[aarongarciah]

This looks like an edge case, yeah. Even if the demos don't need them, I think adding some of the CSS properties like max-width: var(--available-width) is worth it.