fix: accordion panel scroll height overflow

[ricardogarim]

Proposed changes (including videos or screenshots)

Pages with collapsed accordion sections containing Select components show a large blank white space at the bottom. In Rocket.Chat, this affects admin settings pages like Accounts, OAuth, and Layout.

Root cause: In #1939, HiddenSelect was moved from inside SelectTrigger to a sibling to fix an accessibility violation. react-aria's HiddenSelect renders a wrapper with position: absolute. Previously, SelectTrigger acted as its containing block. After the move, the panel (position: static) no longer contains it, so it positions relative to the nearest positioned ancestor outside the panel (e.g., a scroll viewport). The collapsed panel's overflow: hidden doesn't clip these escaped elements, and they inflate the scroll container's scrollHeight.

Fix: Adding position: relative to the panel makes it the containing block, so overflow: hidden properly clips all descendants. One-line CSS change, no DOM modifications, no impact on expand/collapse animations.

Issue(s)

CORE-2202

Regression from #1939.

Steps to reproduce

1. Log in as an admin
2. Open /admin/settings/Accounts
3. Scroll down to the end of the page content
4. Observe the area below the last accordion item

Actual result: A large blank white area is shown after the last settings item, making the page look partially empty / over-scrolled.

Expected result: The settings content should fill the available page body correctly, and the scrollable area should end after the last item without a large blank region.

Further comments

Investigation

The bug appeared between Rocket.Chat 8.4.0 (fuselage 0.76.0) and 8.5.0-develop (fuselage 0.78.0). Several hypotheses were tested and eliminated before identifying the root cause:

What we tested	Outcome
PageScrollableContent has a hardcoded height: 50vh	Ruled out — existed since the component was created, unrelated to the regression
overlayscrollbars bumped from 2.11.4 to 2.11.5	Ruled out — deep-diffed the JS, only one functional change (body-element-only fix), swapping the library files back didn't help
OverlayScrollbars initialization changed from initialize(root) to initialize({target: root}) (Rocket.Chat PR #40391)	Ruled out — reverted the call, rebuilt, verified the bundle had the change, bug persisted
@rocket.chat/css-in-js upgraded from 0.31.25 to 0.32.0 (per-document WeakMap refactor)	Ruled out — the refactor is functionally equivalent for single-document usage
Fuselage accordion CSS changed between 0.76 and 0.78	Ruled out — panel rules are byte-for-byte identical
Meteor upgraded from 3.4 to 3.4.1	Ruled out — eliminated by narrowing the exact commit via git bisect

What confirmed the root cause: Git bisect across commits between 8.4.0 and develop narrowed the regression to commit 305a24255f (fuselage 0.76 -> 0.77 upgrade). Inspecting all changes in that fuselage release led to #1939, where HiddenSelect was moved out of SelectTrigger. Browser inspection confirmed the HiddenSelect wrapper's containing block is the OverlayScrollbars viewport instead of the accordion panel, causing the scroll height inflation.

[changeset-bot]

🦋 Changeset detected

Latest commit: e7c3c6d

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@rocket.chat/fuselage	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[CLAassistant]

All committers have signed the CLA.