🎨 Palette: Improve notification button focus accessibility

[anchapin]

💡 What: Changed :focus to :focus-visible for notification buttons.
🎯 Why: To prevent unsightly focus outlines from appearing when users click buttons with a mouse/touch, while retaining them for keyboard navigation.
📸 Before/After: Outlines used to appear on mouse click; now they only appear on keyboard focus.
♿ Accessibility: Ensures focus outlines are only shown when navigating via keyboard, reducing visual noise for mouse users and encouraging developers to keep focus styles intact rather than removing them entirely.

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PR created automatically by Jules for task 6516025862525388641 started by @anchapin

Summary by Sourcery

Enhancements:

• Adjust notification button focus styles to only appear on :focus-visible, aligning visual focus outlines with keyboard navigation rather than all pointer interactions.

[google-labs-jules]

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[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Replaces generic :focus styles on notification buttons with :focus-visible to preserve keyboard focus outlines while avoiding outlines on mouse/touch clicks.

File-Level Changes

Change	Details	Files
Restrict focus outlines on notification buttons to keyboard-visible focus using :focus-visible instead of :focus.	Updated focus selector for notification action button from :focus to :focus-visible while keeping outline styling unchanged Updated focus selector for notification close button from :focus to :focus-visible while keeping outline styling unchanged	frontend/src/components/NotificationSystem/NotificationSystem.css

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[sourcery-ai]

Hey - I've left some high level feedback:

• Switching from :focus to :focus-visible drops focus styling in browsers that don’t support :focus-visible; consider adding a fallback (e.g., :focus, :focus-visible or a .focus-visible polyfill) to preserve accessibility across older browsers.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Switching from `:focus` to `:focus-visible` drops focus styling in browsers that don’t support `:focus-visible`; consider adding a fallback (e.g., `:focus, :focus-visible` or a `.focus-visible` polyfill) to preserve accessibility across older browsers.

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[Copilot]

Pull request overview

Updates notification button focus styling to use :focus-visible so focus outlines are intended to appear for keyboard navigation rather than mouse/touch interaction.

Changes:

• Replace .notification-*-btn:focus selectors with .notification-*-btn:focus-visible in NotificationSystem component styles.

[Copilot]

Switching these rules from :focus to :focus-visible won’t actually prevent focus outlines on mouse click in this app, because the global stylesheet still applies button:focus { outline: ... } (see frontend/src/index.css:50-53). On mouse click, :focus-visible won’t match, so the global :focus outline will show instead. To achieve the intended behavior while preserving fallback, consider keeping a :focus style for non-supporting browsers and adding a :focus:not(:focus-visible) override to remove the outline for mouse/touch focus (or otherwise overriding the global button:focus for these button classes).