Apple's Safari Technology Preview 243 Addresses Critical Accessibility and CSS Bugs

Breaking: Apple Ships Major Update to Safari Technology Preview

Apple has released Safari Technology Preview 243, a significant update for developers and early adopters running macOS Tahoe and macOS Sequoia. The build includes critical fixes for accessibility, particularly for VoiceOver users, alongside performance improvements in CSS handling.

Version 243 can be downloaded directly or updated via System Settings > General > Software Update. This release incorporates WebKit changes from commit 310600 to 312007.

Key Accessibility Resolutions

"This update addresses several issues that impacted users relying on assistive technologies," says an Apple WebKit engineer. Notably, a bug that prevented the contextmenu event from firing inside iframes for keyboard or VoiceOver actions (e.g., VO+Shift+M) has been fixed (bug 164128676).

Additionally, color picker inputs can now be activated via VoiceOver's press action (bug 172218114). The fix for aria-hidden invalidation when focus enters a hidden subtree (bug 174449524) improves dynamic content experiences. Base <select> elements also see better VoiceOver support, including popover closure and correct positioning with CSS transforms (bug 175058883).

Animation Corrections

Two animation bugs have been squashed. The first ensured !important declarations properly override CSS animation values when transitions run on the same property (bug 174367827). The second fixed identity matrix decomposition generating invalid quaternions, which caused incorrect transform animations (bug 174813328).

CSS Enhancements and Bug Fixes

Safari Technology Preview 243 introduces support for contain: style applying to CSS quote counters (per CSS Containment Level 2) and the insert keyword for text-autospace. Dozens of layout issues have been resolved, including cases where box-shadow now works on display: table-row elements, and clip-path: inset() renders correctly at all sizes.

Performance-wise, pages using :where and :is selectors will load faster. A notable fix corrects text-indent with calc() percentages—previously, percentage components were incorrectly treated as zero for intrinsic sizing (bug 97025949).

Other resolved issues include errors in flex layout using the specified flex-basis instead of the used value, incorrect element positioning with anonymous block containers, and fit-content height miscalculations for out-of-flow content. Quirks mode percentage size resolution in flex items has also been fixed.

Background

The Safari Technology Preview is Apple’s experimental browser, offering a preview of upcoming WebKit features and bug fixes. It runs alongside the stable Safari and is intended for developers to test their sites with bleeding-edge specs.

This release comes as Apple continues to push for a more accessible web, with VoiceOver being a cornerstone of iOS and macOS assistive technology. The CSS containment spec (Level 2) allows developers to limit rendering scope for performance.

What This Means

For developers, these fixes reduce cross-browser compatibility gaps, especially with the contextmenu event and aria-hidden subtrees. The VoiceOver improvements ensure users with disabilities can interact with web apps more reliably.

The CSS fixes, particularly for flex layout and clip-path, will help designers avoid subtle rendering bugs. The performance boost from improved :where/:is selectors benefits all users. "We're committed to making the web more robust and inclusive," adds the WebKit team. Developers should test their sites against this build to ensure compatibility ahead of future Safari releases.