Background image control: Remove duplicated focus ring

[t-hamano]

What?

Part of #80138

Removes the custom box-shadow focus outline from the Image button in the Background panel.

Why?

The Button component now renders its focus ring with outline, so the component's own focus ring and this custom box-shadow are both drawn, resulting in a double focus ring.

Testing Instructions

1. Insert a Group block.
2. Open the Block Inspector > Background panel.
3. Focus the Image button and confirm only a single focus ring is rendered.

Screenshots or screencast

Note that to compare the focus outline with other buttons, I am applying a focus state to the relevant buttons using the browser developer tools.

Before	After

Use of AI Tools

Claude Code was used to create the commit and draft this pull request description. The code change itself was authored and verified manually.

[github-actions]

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Co-authored-by: t-hamano <wildworks@git.wordpress.org>
Co-authored-by: tyxla <tyxla@git.wordpress.org>

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[tyxla]

LGTM, thanks @t-hamano 🙌

[github-actions]

Size Change: -13 B (0%)

Total Size: 7.75 MB

📦 View Changed

Filename	Size	Change
build/styles/block-editor/style-rtl.css	20 kB	-4 B (-0.02%)
build/styles/block-editor/style-rtl.min.css	17 kB	-3 B (-0.02%)
build/styles/block-editor/style.css	20 kB	-4 B (-0.02%)
build/styles/block-editor/style.min.css	17 kB	-2 B (-0.01%)

_{compressed-size-action}

[noruzzamans]

Tested! Confirms the fix works as expected. Focusing the Image button in the Background panel now shows only a single focus ring, no duplication.

Screen.Recording.2026-07-24.at.2.51.55.PM.mov

[github-actions]

Flaky tests detected in 8d0ddc9.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/30078050398
📝 Reported issues:

• [Flaky Test] should update the HTML only for the latest navigation #78835 in /test/e2e/specs/interactivity/router-navigate.spec.ts

[github-actions]

I just cherry-picked this PR to the wp/7.1 branch to get it included in the next release: 7a561a8