[select] Glitchy `alignItemWithTrigger` behavior when Popup has max-height

[mirka]

Bug report

Current behavior

The alignItemWithTrigger behavior of the Select.Positioner can be glitchy when there's a max-height on the Select.Popup and the list is overflowing. It can look as if the popover is scrolling away from the trigger.

Expected behavior

Scrolling is contained within the overflowing list.

Reproducible example

https://stackblitz.com/edit/ypr9pa86?file=src%2Findex.module.css

CleanShot.2025-12-03.at.08-08-08.mp4

Base UI version

1.0.0-beta.7

Which browser are you using?

Chrome

Which OS are you using?

Mac OS

[atomiks]

We don't recommend changing the max-height here as the tall viewport (that spans the entire screen) matches native behavior, allowing users to see many options at the same time after expanding it. What's the main reason you want to change this?