Add shadow to Popover component

[Copilot]

Closes https://github.com/github/primer/issues/6120

Adds box-shadow: var(--shadow-floating-small) to Popover, aligning it with Dialog and Overlay components.

Before:
Popover displayed with border only, no depth differentiation from page content.

After:

Changelog

New

Changed

• Popover.Content now renders with floating shadow using --shadow-floating-small design token

Removed

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

Visual regression tests will capture the shadow addition. Existing functionality unchanged.

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

Popover should have a shadow using the shadow css variable --shadow-floating-small

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[changeset-bot]

🦋 Changeset detected

Latest commit: 84bacb2

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

This PR includes changesets to release 1 package

Name	Type
@primer/react	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

[lukasoppermann]

This closes https://github.com/github/primer/issues/6120

[github-actions]

👋 Hi, this pull request contains changes to the source code that github/github-ui depends on. If you are GitHub staff, test these changes with github/github-ui using the integration workflow. Or, apply the integration-tests: skipped manually label to skip these checks.

[Copilot]

Pull Request Overview

This PR adds a floating shadow to the Popover component to align its visual design with Dialog and Overlay components, improving depth perception and visual hierarchy.

Key Changes:

• Replaces the border with box-shadow: var(--shadow-floating-small) design token
• Updates all visual regression test snapshots across themes and color modes

Reviewed Changes

Copilot reviewed 2 out of 29 changed files in this pull request and generated 1 comment.

File	Description
packages/react/src/Popover/Popover.module.css	Removes border property and adds box-shadow using the --shadow-floating-small design token
.playwright/snapshots/components/Popover.test.ts-snapshots/*.png	Updates visual regression test snapshots for all theme variants (light, dark, high-contrast, colorblind, tritanopia, dimmed) to reflect the shadow addition
.changeset/gentle-peas-kick.md	Adds changeset documenting the patch-level change

[Copilot]

The border property has been removed entirely. According to the PR description, the goal is to add shadow to align with Dialog and Overlay components, but this change removes the existing border. Consider whether the border should be retained alongside the shadow, or if this is intentional. If intentional, the PR description should clearly state that the border is being replaced (not just that shadow is being added).

Suggested change

	border-radius: var(--borderRadius-medium);
	border-radius: var(--borderRadius-medium);
	border: 1px solid var(--borderColor-default);

[primer-integration]

👋 Hi from github/github-ui! Your integration PR is ready: https://github.com/github/github-ui/pull/6889

[primer-integration]

🟢 ci completed with status success.