What's New in Safari Technology Preview 243? Key Fixes and Features Explained

Safari Technology Preview 243 is now available for download, delivering a bundle of bug fixes and improvements for macOS Tahoe and macOS Sequoia. This update focuses on accessibility enhancements, CSS refinements, and animation corrections. If you already have the Preview installed, you can update via System Settings > General > Software Update. Below, we answer the most common questions about this release.

What accessibility issues have been resolved?

Several important accessibility problems are fixed in this release:

What's New in Safari Technology Preview 243? Key Fixes and Features Explained — Source: webkit.org

The contextmenu event now fires correctly for elements inside <iframe> when triggered by keyboard or assistive technology actions like VoiceOver’s VO+Shift+M.
Color picker inputs can now be activated using VoiceOver’s press action.
Invalidation of aria-hidden="true" is properly handled when focus lands inside the aria-hidden subtree.
VoiceOver support for basic <select> elements is improved, including closing the popover upon selection and correcting accessibility path positioning even when CSS transforms are present.

These fixes ensure a smoother experience for users relying on assistive technologies.

What animation-related bugs were corrected?

Two animation issues are addressed:

!important declarations now correctly override CSS animation values when CSS transitions are also running on the same property, resolving a conflict that previously ignored the !important rule.
Transform animations using identity matrix decomposition no longer generate invalid quaternions, which was causing incorrect transform animations. The fix ensures smooth and accurate animated transforms.

What new CSS features are introduced?

Two new CSS capabilities debut in this release:

Support for contain: style applying to CSS quote counters, as specified in CSS Containment Level 2. This allows developers to better isolate styling containment for quote-related properties.
Support for the insert keyword for the text-autospace property, giving more control over automatic spacing adjustments in text.

Which CSS layout and rendering bugs were fixed?

A wide range of layout and rendering issues have been resolved:

Flex layout now uses the used flex-basis instead of the specified value for definiteness evaluation.
Element positioning is corrected when the containing block is an anonymous block.
box-shadow now works on display: table-row elements.
text-indent with calc() containing percentages correctly treats percentage components as zero for intrinsic size contributions.
Out-of-flow content with fit-content now has the correct height.
Percentage size resolution in flex items works correctly in quirks mode.
clip-path: inset() with border-radius renders accurately at various sizes.
-webkit-box flexbox emulation no longer mis-sizes children inside <fieldset> elements.
Elements with display: table now layout correctly when borders are present.
Elements with border, position: absolute, and aspect-ratio: 1 are rendered as squares, as expected.

Were there any performance improvements?

Yes, one notable performance enhancement: pages using the :where and :is selectors now see improved performance. This optimization reduces selector matching overhead, making pages that rely heavily on these pseudo-classes render faster.

How can I install or update to Safari Technology Preview 243?

If you are using macOS Tahoe or macOS Sequoia, you can download Safari Technology Preview 243 from the official Safari Technology Preview website. If you already have a previous version installed, simply navigate to System Settings > General > Software Update to update. The update is free and available to all developers and enthusiasts who want to test the latest WebKit features.

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