Simplify PageLayout CSS by removing redundant margin resets

[Copilot]

The PR #7433 CSS changes contained redundant declarations that can be removed while preserving the SSR layout shift fix.

Changes

Removed 32 lines of redundant CSS from PageLayout.module.css:

• Base .PaneWrapper: Removed explicit margin: 0 declarations (already default)
• Narrow viewport: Removed duplicate [data-position='end'] and [data-position='start'] selectors - base styles handle narrow correctly
• All viewports: Removed unnecessary zero margin resets where the opposite side already sets the spacing margin

Essential changes preserved:

• Base [data-position] stacked layout styles
• Desktop @media (min-width: 768px) side-by-side overrides
• .Pane[data-resizable] fix using var(--pane-width-size)

Changelog

Changed

• Simplified PageLayout.module.css by removing 32 lines of redundant CSS

Rollout strategy

• Patch release
• Minor release
• Major release; if selected, include a written rollout or migration plan
• None; if selected, include a brief description as to why

Testing & Reviewing

CSS linting, build, type checking, and format checking all pass. The diff is now minimal and focused on essential changes only.

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Storybook)
• Changes are SSR compatible
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge
• (GitHub staff only) Integration tests pass at github/github (Learn more about how to run integration tests)

Original prompt

Problem

The current changes in PR #7433 have redundant CSS that can be removed to minimize the diff while still fixing the SSR layout shift issue.

Changes Needed

Simplify the CSS changes in packages/react/src/PageLayout/PageLayout.module.css to only include what's essential:

1. Remove redundant margin resets from base .PaneWrapper

Remove these lines that were added (margins are already 0 by default):

margin-top: 0;
margin-bottom: 0;

2. Remove redundant narrow viewport overrides

Inside @media (--viewportRange-narrow), remove the duplicate [data-position='end'] and [data-position='start'] selectors since the base styles now handle narrow viewports correctly. The [data-position-narrow='end'] and [data-position-narrow='start'] selectors should remain for explicit narrow overrides.

Also remove the unnecessary margin-left: 0 and margin-right: 0 from narrow selectors - these are already 0.

3. Remove unnecessary margin resets from regular/wide viewport selectors

Remove margin-right: 0 and margin-left: 0 from:

• [data-position-regular='end']
• [data-position-regular='start']
• [data-position-wide='end']
• [data-position-wide='start']

These aren't needed since we're explicitly setting the correct margin on the opposite side.

4. Keep the essential changes

Keep:

• Base [data-position='end'] and [data-position='start'] with stacked layout styles
• Desktop @media screen and (min-width: 768px) overrides for [data-position='end'] and [data-position='start']
• The .Pane[data-resizable] fix: width: var(--pane-width-size) instead of width: 100%

Goal

Reduce the diff from ~42 additions/18 deletions to the minimal set of changes needed to fix the SSR layout shift, making it easier to review and reducing risk of unintended side effects.

This pull request was created from Copilot chat.

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