Safari Technology Preview Release 243 is here with important improvements for developers. This update, available for macOS Tahoe and Sequoia, addresses several bugs and introduces new CSS capabilities. In this Q&A, we break down the most significant changes, from accessibility enhancements to layout fixes, so you can quickly understand what's new.
How can I get Safari Technology Preview 243, and what does it include?
You can download Safari Technology Preview 243 for macOS Tahoe and macOS Sequoia. If you already have the preview installed, simply navigate to System Settings → General → Software Update to upgrade. This release incorporates WebKit changes from revision 310600 to 312007, meaning it includes a wide range of fixes and features across accessibility, animations, and CSS. The update is free for all registered Apple developers and offers a sneak peek at upcoming web technologies.
What accessibility issues were resolved in this release?
Several accessibility bugs have been fixed to improve assistive technology interactions. Notably, the contextmenu event now works correctly for elements inside iframes when triggered by keyboard or VoiceOver actions (e.g., VO+Shift+M). Color picker inputs can be activated using VoiceOver’s press action again. The invalidation of aria-hidden="true" when focus lands inside the hidden subtree has been resolved. Additionally, VoiceOver support for basic <select> elements has been improved, including proper closing of the popover after selection and correct accessibility path positioning even when CSS transforms are applied. These changes make the browser more usable for people relying on assistive technologies.
What animation-related bugs were fixed?
Two key animation issues have been resolved. First, !important declarations now correctly override CSS animation values when CSS transitions are also running on the same property. Previously, the important flag was sometimes ignored, causing conflicting behavior. Second, a bug in identity matrix decomposition generated invalid quaternions, leading to incorrect transform animations. This fix ensures that transforms animate smoothly and accurately, particularly when using 3D rotations or complex matrix operations. Developers should test their animations after updating to confirm expected behavior.
What new CSS features were introduced?
Safari Technology Preview 243 adds two CSS features. First, it now supports contain: style applying to CSS quote counters, as specified in CSS Containment Level 2. This allows better performance by limiting style recalculations to the contained subtree, especially when using quotes generated by content properties. Second, the insert keyword for the text-autospace property has been added. This property controls automatic spacing around ideographic and Latin text, and the insert value ensures consistent spacing adjustments. These features help developers create more robust and efficient layouts.
What are some notable CSS layout fixes?
Several layout issues have been corrected. Flexbox now uses the used flex-basis instead of the specified value for definiteness evaluation, improving responsiveness. Element positioning is fixed when the containing block is an anonymous block. Box-shadow now works on display: table-row elements. The text-indent property with calc() containing percentages correctly treats percentage components as zero for intrinsic size contributions. Out-of-flow content with fit-content now has correct height. Percentage size resolution in flex items in quirks mode is fixed. Also, clip-path: inset() border-radius renders correctly at various sizes. The -webkit-box flexbox emulation now sizes children properly inside <fieldset>. Additionally, performance improved on pages using :where and :is selectors.
Were there any other rendering improvements?
Yes, other rendering fixes include correcting layout for display: table elements with borders, and ensuring elements with border, position: absolute, and aspect-ratio: 1 render as squares. These changes address edge cases that could cause visual glitches or misaligned content. Developers working with complex layouts—especially those combining tables, absolute positioning, and aspect ratios—should see more predictable results. The update also includes general stability improvements under the hood, making the preview a more reliable testing environment for cutting-edge web features.