Add support for reduced transparency in accessibility settings

[mrleemurray]

Introduce a new accessibility feature that allows users to reduce transparency and blur effects for improved performance. This change includes updates to the configuration settings, event handling, and CSS class management to reflect the user's preferences. Testing can be done by changing the workbench.reduceTransparency setting and observing the changes in the UI.

Addresses: #294977

[vs-code-engineering]

📬 CODENOTIFY

The following users are being notified based on files changed in this PR:

@bpasero

Matched files:

• src/vs/workbench/browser/workbench.contribution.ts

[Copilot]

Pull request overview

Adds a new accessibility setting to reduce transparency/blur effects and wires it through the platform accessibility service so the workbench can react via a root CSS class (with theme-2026 providing the initial styling adjustments).

Changes:

• Register new setting workbench.reduceTransparency (on/off/auto) under accessibility settings.
• Extend IAccessibilityService + AccessibilityService to track reduced transparency (config + OS media query), expose an event, and toggle monaco-reduce-transparency on the workbench root.
• Add browser unit tests for reduced-transparency behavior and update the test accessibility service stub; update theme-2026 CSS to remove blur/transparency effects when the class is present.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/vs/workbench/browser/workbench.contribution.ts	Adds the workbench.reduceTransparency configuration schema entry.
src/vs/platform/accessibility/common/accessibility.ts	Extends the accessibility service interface with reduced-transparency API.
src/vs/platform/accessibility/browser/accessibilityService.ts	Implements reduced-transparency detection, eventing, and root CSS class toggling.
src/vs/platform/accessibility/test/common/testAccessibilityService.ts	Updates the test stub to satisfy the expanded interface.
src/vs/platform/accessibility/test/browser/accessibilityService.test.ts	Adds unit tests for reduced transparency (and covers reduced motion basics).
extensions/theme-2026/themes/styles.css	Applies reduced-transparency styling overrides when monaco-reduce-transparency is present.