Safari Technology Preview 243 brings a host of improvements to WebKit, focusing on accessibility, animation reliability, and CSS enhancements. This release is available for macOS Tahoe and macOS Sequoia, offering developers and early adopters a chance to test the latest rendering engine changes. Below, we answer common questions about the update, covering download instructions, resolved issues, and new capabilities.
What is Safari Technology Preview 243 and how can I download or update it?
Safari Technology Preview 243 is the latest experimental version of Apple’s browser engine, WebKit. It is designed for developers to test upcoming features and fixes before they reach the stable Safari browser. This release is compatible with macOS Tahoe and macOS Sequoia. If you already have Safari Technology Preview installed, updating is straightforward: open System Settings, navigate to General, then Software Update, and follow the prompts. For a fresh install, visit the official Safari Technology Preview download page. The build includes WebKit changes between versions 310600 and 312007, encompassing numerous bug fixes and feature additions across accessibility, animations, and CSS.
What accessibility issues were resolved in this release?
Several accessibility bugs have been squashed in Safari Technology Preview 243. One key fix ensures that the contextmenu event now fires correctly for elements inside <iframe> when triggered via keyboard or assistive technologies like VoiceOver (VO+Shift+M). Additionally, color picker inputs can now be activated using VoiceOver’s press action. The update also addresses invalidation of aria-hidden="true" when focus lands inside the hidden subtree, improving screen reader behavior. For <select> elements, VoiceOver support has been enhanced: the popover now closes upon selection, and accessibility path positioning is corrected when CSS transforms are applied. These changes make web interactions more reliable for users relying on assistive tools.
What animation-related bugs were fixed?
Two notable 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 cascade could fail, leading to unexpected behavior. Second, an error in identity matrix decomposition generated invalid quaternions, which caused incorrect transform animations. This fix ensures that 3D rotations and other transform-based animations behave as intended. Both improvements contribute to smoother, more predictable animation performance in web applications.
What new CSS features have been added?
Release 243 introduces two CSS enhancements. Support has been added for contain: style applying to CSS quote counters, as specified in CSS Containment Level 2. This allows developers to limit the scope of style calculations, potentially boosting performance on complex pages. Additionally, the insert keyword is now supported for the text-autospace property, giving finer control over spacing between characters in East Asian typography. These additions align with evolving web standards and offer more precise styling options.
What CSS rendering bugs were addressed?
A wide range of CSS rendering bugs have been fixed. Flex layout now uses the used flex-basis instead of the specified value for definiteness evaluation, preventing sizing errors. Element positioning is corrected 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 height now calculates properly. Percentage size resolution in flex items under quirks mode is fixed. clip-path: inset() border-radius values render correctly at various sizes. -webkit-box flexbox emulation now sizes children correctly inside <fieldset>. Improved performance for pages using :where and :is selectors. display: table elements with borders have correct layout. And elements with border, position: absolute, and aspect-ratio: 1 now render as squares. These fixes enhance visual consistency across many CSS scenarios.
How does this release improve CSS performance and selector handling?
This update brings a significant performance boost for pages heavy on selector complexity. The fix for :where and :is pseudo-classes reduces overhead when these selectors are used extensively. Additionally, the adoption of CSS Containment Level 2 for style containment can limit recalculations. Together, these changes help web applications run faster, especially those with large stylesheets or dynamic DOM updates. Developers using advanced selector patterns should notice smoother rendering and lower CPU usage, making this release a valuable upgrade for performance-sensitive projects.