…56630)

## Summary
This PR is part of the cascade performance improvement
work(elastic#255745), culled from
elastic#256037.

Adds CSS `contain: layout style` and `overflowAnchor: none` to the
DataCascade virtualized scroll container and row wrappers, scoping
layout/style invalidation so that row DOM mutations during scrolling
cannot trigger full-document relayouts.

## Changes

- **`data_cascade_impl.styles.tsx`** (`cascadeTreeGridBlock`): add
`contain: 'layout style'` and `overflowAnchor: 'none'`
- **`cascade_row.styles.ts`** (`rowWrapper`): add `contain: 'layout
style'`

## Performance impact (Generated by Cursor)

Compared using Chrome DevTools trace profiles (baseline vs this PR)
during scroll interaction:

| Metric (per-second normalized) | Baseline | PR | Change |
|---|---|---|---|
| Layout total time | 3,737 us/s | 1,686 us/s | **-55%** |
| Full (non-partial) layouts | 9 | **0** | **-100%** |
| UpdateLayoutTree time | 63,821 us/s | 38,009 us/s | **-40%** |
| Paint time | 4,392 us/s | 1,025 us/s | **-77%** |
| Layout invalidations | 13.3/s | 6.7/s | **-50%** |
| Style recalc triggers | 20.6/s | 9.6/s | **-54%** |
| Long task (>50ms) time | 459,137 us/s | 237,431 us/s | **-48%** |
| Avg frame time | 5.9 ms | 3.4 ms | **-42%** |
| Worst-case frame | 203 ms | 73 ms | **-64%** |
| Max dirty objects/layout | 864 | 414 | **-52%** |
| Layout shifts | 4 | 2 | **-50%** |

The headline result is **complete elimination of full document layouts**
during scroll. The two nested containment boundaries (container + rows)
ensure layout invalidation from virtualizer DOM mutations stays confined
to the contained subtree, turning expensive full-document relayouts into
cheap scoped partial layouts. `overflowAnchor: none` prevents additional
layout passes from scroll anchoring adjustments during DOM recycling.

<!--
### Checklist

Check the PR satisfies following conditions.

Reviewers should verify this PR satisfies this list as well.

- [ ] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/src/platform/packages/shared/kbn-i18n/README.md)
- [ ]
[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials
- [ ] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [ ] If a plugin configuration key changed, check if it needs to be
allowlisted in the cloud and added to the [docker
list](https://github.com/elastic/kibana/blob/main/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)
- [ ] This was checked for breaking HTTP API changes, and any breaking
changes have been approved by the breaking-change committee. The
`release_note:breaking` label should be applied in these situations.
- [ ] [Flaky Test
Runner](https://ci-stats.kibana.dev/trigger_flaky_test_runner/1) was
used on any tests changed
- [ ] The PR description includes the appropriate Release Notes section,
and the correct `release_note:*` label is applied per the
[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)
- [ ] Review the [backport
guidelines](https://docs.google.com/document/d/1VyN5k91e5OVumlc0Gb9RPa3h1ewuPE705nRtioPiTvY/edit?usp=sharing)
and apply applicable `backport:*` labels.

### Identify risks

Does this PR introduce any risks? For example, consider risks like hard
to test bugs, performance regression, potential of data loss.

Describe the risk, its severity, and mitigation for each identified
risk. Invite stakeholders and evaluate how to proceed before merging.

- [ ] [See some risk
examples](https://github.com/elastic/kibana/blob/main/RISK_MATRIX.mdx)
- [ ] ...

-->

(cherry picked from commit 52968c7)

…6630) (#256800)

# Backport

This will backport the following commits from `main` to `9.3`:
- [[Cascade] Specify strict layout guidance for rows and cell
(#256630)](#256630)

<!--- Backport version: 9.6.6 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sorenlouv/backport)

<!--BACKPORT [{"author":{"name":"Eyo O.
Eyo","email":"7893459+eokoneyo@users.noreply.github.com"},"sourceCommit":{"committedDate":"2026-03-09T21:34:44Z","message":"[Cascade]
Specify strict layout guidance for rows and cell (#256630)\n\n##
Summary\nThis PR is part of the cascade performance
improvement\nwork(#255745),
culled from\nhttps://github.com//pull/256037.\n\nAdds CSS
`contain: layout style` and `overflowAnchor: none` to the\nDataCascade
virtualized scroll container and row wrappers, scoping\nlayout/style
invalidation so that row DOM mutations during scrolling\ncannot trigger
full-document relayouts.\n\n## Changes\n\n-
**`data_cascade_impl.styles.tsx`** (`cascadeTreeGridBlock`):
add\n`contain: 'layout style'` and `overflowAnchor: 'none'`\n-
**`cascade_row.styles.ts`** (`rowWrapper`): add `contain:
'layout\nstyle'`\n\n## Performance impact (Generated by
Cursor)\n\nCompared using Chrome DevTools trace profiles (baseline vs
this PR)\nduring scroll interaction:\n\n| Metric (per-second normalized)
| Baseline | PR | Change |\n|---|---|---|---|\n| Layout total time |
3,737 us/s | 1,686 us/s | **-55%** |\n| Full (non-partial) layouts | 9 |
**0** | **-100%** |\n| UpdateLayoutTree time | 63,821 us/s | 38,009 us/s
| **-40%** |\n| Paint time | 4,392 us/s | 1,025 us/s | **-77%** |\n|
Layout invalidations | 13.3/s | 6.7/s | **-50%** |\n| Style recalc
triggers | 20.6/s | 9.6/s | **-54%** |\n| Long task (>50ms) time |
459,137 us/s | 237,431 us/s | **-48%** |\n| Avg frame time | 5.9 ms |
3.4 ms | **-42%** |\n| Worst-case frame | 203 ms | 73 ms | **-64%** |\n|
Max dirty objects/layout | 864 | 414 | **-52%** |\n| Layout shifts | 4 |
2 | **-50%** |\n\nThe headline result is **complete elimination of full
document layouts**\nduring scroll. The two nested containment boundaries
(container + rows)\nensure layout invalidation from virtualizer DOM
mutations stays confined\nto the contained subtree, turning expensive
full-document relayouts into\ncheap scoped partial layouts.
`overflowAnchor: none` prevents additional\nlayout passes from scroll
anchoring adjustments during DOM
recycling.\n\n","sha":"52968c7bcc3bb75f83fa57c3bbb8fcffaa260454","branchLabelMapping":{"^v9.4.0$":"main","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["release_note:skip","Team:SharedUX","backport:version","v9.4.0","v9.3.2"],"title":"[Cascade]
Specify strict layout guidance for rows and
cell","number":256630,"url":"https://github.com/elastic/kibana/pull/256630","mergeCommit":{"message":"[Cascade]
Specify strict layout guidance for rows and cell (#256630)\n\n##
Summary\nThis PR is part of the cascade performance
improvement\nwork(#255745),
culled from\nhttps://github.com//pull/256037.\n\nAdds CSS
`contain: layout style` and `overflowAnchor: none` to the\nDataCascade
virtualized scroll container and row wrappers, scoping\nlayout/style
invalidation so that row DOM mutations during scrolling\ncannot trigger
full-document relayouts.\n\n## Changes\n\n-
**`data_cascade_impl.styles.tsx`** (`cascadeTreeGridBlock`):
add\n`contain: 'layout style'` and `overflowAnchor: 'none'`\n-
**`cascade_row.styles.ts`** (`rowWrapper`): add `contain:
'layout\nstyle'`\n\n## Performance impact (Generated by
Cursor)\n\nCompared using Chrome DevTools trace profiles (baseline vs
this PR)\nduring scroll interaction:\n\n| Metric (per-second normalized)
| Baseline | PR | Change |\n|---|---|---|---|\n| Layout total time |
3,737 us/s | 1,686 us/s | **-55%** |\n| Full (non-partial) layouts | 9 |
**0** | **-100%** |\n| UpdateLayoutTree time | 63,821 us/s | 38,009 us/s
| **-40%** |\n| Paint time | 4,392 us/s | 1,025 us/s | **-77%** |\n|
Layout invalidations | 13.3/s | 6.7/s | **-50%** |\n| Style recalc
triggers | 20.6/s | 9.6/s | **-54%** |\n| Long task (>50ms) time |
459,137 us/s | 237,431 us/s | **-48%** |\n| Avg frame time | 5.9 ms |
3.4 ms | **-42%** |\n| Worst-case frame | 203 ms | 73 ms | **-64%** |\n|
Max dirty objects/layout | 864 | 414 | **-52%** |\n| Layout shifts | 4 |
2 | **-50%** |\n\nThe headline result is **complete elimination of full
document layouts**\nduring scroll. The two nested containment boundaries
(container + rows)\nensure layout invalidation from virtualizer DOM
mutations stays confined\nto the contained subtree, turning expensive
full-document relayouts into\ncheap scoped partial layouts.
`overflowAnchor: none` prevents additional\nlayout passes from scroll
anchoring adjustments during DOM
recycling.\n\n","sha":"52968c7bcc3bb75f83fa57c3bbb8fcffaa260454"}},"sourceBranch":"main","suggestedTargetBranches":["9.3"],"targetPullRequestStates":[{"branch":"main","label":"v9.4.0","branchLabelMappingKey":"^v9.4.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/256630","number":256630,"mergeCommit":{"message":"[Cascade]
Specify strict layout guidance for rows and cell (#256630)\n\n##
Summary\nThis PR is part of the cascade performance
improvement\nwork(#255745),
culled from\nhttps://github.com//pull/256037.\n\nAdds CSS
`contain: layout style` and `overflowAnchor: none` to the\nDataCascade
virtualized scroll container and row wrappers, scoping\nlayout/style
invalidation so that row DOM mutations during scrolling\ncannot trigger
full-document relayouts.\n\n## Changes\n\n-
**`data_cascade_impl.styles.tsx`** (`cascadeTreeGridBlock`):
add\n`contain: 'layout style'` and `overflowAnchor: 'none'`\n-
**`cascade_row.styles.ts`** (`rowWrapper`): add `contain:
'layout\nstyle'`\n\n## Performance impact (Generated by
Cursor)\n\nCompared using Chrome DevTools trace profiles (baseline vs
this PR)\nduring scroll interaction:\n\n| Metric (per-second normalized)
| Baseline | PR | Change |\n|---|---|---|---|\n| Layout total time |
3,737 us/s | 1,686 us/s | **-55%** |\n| Full (non-partial) layouts | 9 |
**0** | **-100%** |\n| UpdateLayoutTree time | 63,821 us/s | 38,009 us/s
| **-40%** |\n| Paint time | 4,392 us/s | 1,025 us/s | **-77%** |\n|
Layout invalidations | 13.3/s | 6.7/s | **-50%** |\n| Style recalc
triggers | 20.6/s | 9.6/s | **-54%** |\n| Long task (>50ms) time |
459,137 us/s | 237,431 us/s | **-48%** |\n| Avg frame time | 5.9 ms |
3.4 ms | **-42%** |\n| Worst-case frame | 203 ms | 73 ms | **-64%** |\n|
Max dirty objects/layout | 864 | 414 | **-52%** |\n| Layout shifts | 4 |
2 | **-50%** |\n\nThe headline result is **complete elimination of full
document layouts**\nduring scroll. The two nested containment boundaries
(container + rows)\nensure layout invalidation from virtualizer DOM
mutations stays confined\nto the contained subtree, turning expensive
full-document relayouts into\ncheap scoped partial layouts.
`overflowAnchor: none` prevents additional\nlayout passes from scroll
anchoring adjustments during DOM
recycling.\n\n","sha":"52968c7bcc3bb75f83fa57c3bbb8fcffaa260454"}},{"branch":"9.3","label":"v9.3.2","branchLabelMappingKey":"^v(\\d+).(\\d+).\\d+$","isSourceBranch":false,"state":"NOT_CREATED"}]}]
BACKPORT-->

Co-authored-by: Eyo O. Eyo <7893459+eokoneyo@users.noreply.github.com>

…56630)

## Summary
This PR is part of the cascade performance improvement
work(elastic#255745), culled from
elastic#256037.

Adds CSS `contain: layout style` and `overflowAnchor: none` to the
DataCascade virtualized scroll container and row wrappers, scoping
layout/style invalidation so that row DOM mutations during scrolling
cannot trigger full-document relayouts.

## Changes

- **`data_cascade_impl.styles.tsx`** (`cascadeTreeGridBlock`): add
`contain: 'layout style'` and `overflowAnchor: 'none'`
- **`cascade_row.styles.ts`** (`rowWrapper`): add `contain: 'layout
style'`

## Performance impact (Generated by Cursor)

Compared using Chrome DevTools trace profiles (baseline vs this PR)
during scroll interaction:

| Metric (per-second normalized) | Baseline | PR | Change |
|---|---|---|---|
| Layout total time | 3,737 us/s | 1,686 us/s | **-55%** |
| Full (non-partial) layouts | 9 | **0** | **-100%** |
| UpdateLayoutTree time | 63,821 us/s | 38,009 us/s | **-40%** |
| Paint time | 4,392 us/s | 1,025 us/s | **-77%** |
| Layout invalidations | 13.3/s | 6.7/s | **-50%** |
| Style recalc triggers | 20.6/s | 9.6/s | **-54%** |
| Long task (>50ms) time | 459,137 us/s | 237,431 us/s | **-48%** |
| Avg frame time | 5.9 ms | 3.4 ms | **-42%** |
| Worst-case frame | 203 ms | 73 ms | **-64%** |
| Max dirty objects/layout | 864 | 414 | **-52%** |
| Layout shifts | 4 | 2 | **-50%** |

The headline result is **complete elimination of full document layouts**
during scroll. The two nested containment boundaries (container + rows)
ensure layout invalidation from virtualizer DOM mutations stays confined
to the contained subtree, turning expensive full-document relayouts into
cheap scoped partial layouts. `overflowAnchor: none` prevents additional
layout passes from scroll anchoring adjustments during DOM recycling.

<!--
### Checklist

Check the PR satisfies following conditions. 

Reviewers should verify this PR satisfies this list as well.

- [ ] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/src/platform/packages/shared/kbn-i18n/README.md)
- [ ]
[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials
- [ ] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [ ] If a plugin configuration key changed, check if it needs to be
allowlisted in the cloud and added to the [docker
list](https://github.com/elastic/kibana/blob/main/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)
- [ ] This was checked for breaking HTTP API changes, and any breaking
changes have been approved by the breaking-change committee. The
`release_note:breaking` label should be applied in these situations.
- [ ] [Flaky Test
Runner](https://ci-stats.kibana.dev/trigger_flaky_test_runner/1) was
used on any tests changed
- [ ] The PR description includes the appropriate Release Notes section,
and the correct `release_note:*` label is applied per the
[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)
- [ ] Review the [backport
guidelines](https://docs.google.com/document/d/1VyN5k91e5OVumlc0Gb9RPa3h1ewuPE705nRtioPiTvY/edit?usp=sharing)
and apply applicable `backport:*` labels.

### Identify risks

Does this PR introduce any risks? For example, consider risks like hard
to test bugs, performance regression, potential of data loss.

Describe the risk, its severity, and mitigation for each identified
risk. Invite stakeholders and evaluate how to proceed before merging.

- [ ] [See some risk
examples](https://github.com/elastic/kibana/blob/main/RISK_MATRIX.mdx)
- [ ] ...

-->

## Summary
This PR is part of the cascade performance improvement
work(#255745), culled from
#256037.

Adds CSS `contain: layout style` and `overflowAnchor: none` to the
DataCascade virtualized scroll container and row wrappers, scoping
layout/style invalidation so that row DOM mutations during scrolling
cannot trigger full-document relayouts.

## Changes

- **`data_cascade_impl.styles.tsx`** (`cascadeTreeGridBlock`): add
`contain: 'layout style'` and `overflowAnchor: 'none'`
- **`cascade_row.styles.ts`** (`rowWrapper`): add `contain: 'layout
style'`

## Performance impact (Generated by Cursor)

Compared using Chrome DevTools trace profiles (baseline vs this PR)
during scroll interaction:

| Metric (per-second normalized) | Baseline | PR | Change |
|---|---|---|---|
| Layout total time | 3,737 us/s | 1,686 us/s | **-55%** |
| Full (non-partial) layouts | 9 | **0** | **-100%** |
| UpdateLayoutTree time | 63,821 us/s | 38,009 us/s | **-40%** |
| Paint time | 4,392 us/s | 1,025 us/s | **-77%** |
| Layout invalidations | 13.3/s | 6.7/s | **-50%** |
| Style recalc triggers | 20.6/s | 9.6/s | **-54%** |
| Long task (>50ms) time | 459,137 us/s | 237,431 us/s | **-48%** |
| Avg frame time | 5.9 ms | 3.4 ms | **-42%** |
| Worst-case frame | 203 ms | 73 ms | **-64%** |
| Max dirty objects/layout | 864 | 414 | **-52%** |
| Layout shifts | 4 | 2 | **-50%** |

The headline result is **complete elimination of full document layouts**
during scroll. The two nested containment boundaries (container + rows)
ensure layout invalidation from virtualizer DOM mutations stays confined
to the contained subtree, turning expensive full-document relayouts into
cheap scoped partial layouts. `overflowAnchor: none` prevents additional
layout passes from scroll anchoring adjustments during DOM recycling.

<!--
### Checklist

Check the PR satisfies following conditions. 

Reviewers should verify this PR satisfies this list as well.

- [ ] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/src/platform/packages/shared/kbn-i18n/README.md)
- [ ]
[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials
- [ ] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [ ] If a plugin configuration key changed, check if it needs to be
allowlisted in the cloud and added to the [docker
list](https://github.com/elastic/kibana/blob/main/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)
- [ ] This was checked for breaking HTTP API changes, and any breaking
changes have been approved by the breaking-change committee. The
`release_note:breaking` label should be applied in these situations.
- [ ] [Flaky Test
Runner](https://ci-stats.kibana.dev/trigger_flaky_test_runner/1) was
used on any tests changed
- [ ] The PR description includes the appropriate Release Notes section,
and the correct `release_note:*` label is applied per the
[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)
- [ ] Review the [backport
guidelines](https://docs.google.com/document/d/1VyN5k91e5OVumlc0Gb9RPa3h1ewuPE705nRtioPiTvY/edit?usp=sharing)
and apply applicable `backport:*` labels.

### Identify risks

Does this PR introduce any risks? For example, consider risks like hard
to test bugs, performance regression, potential of data loss.

Describe the risk, its severity, and mitigation for each identified
risk. Invite stakeholders and evaluate how to proceed before merging.

- [ ] [See some risk
examples](https://github.com/elastic/kibana/blob/main/RISK_MATRIX.mdx)
- [ ] ...

-->