Safari Technology Preview 243: Key Fixes and New Features Explained
Apple has released Safari Technology Preview 243, an experimental browser build for macOS Tahoe and macOS Sequoia. This update brings a host of refinements to accessibility, CSS capabilities, and animation handling. Below, we break down the most important changes in a Q&A format to help you quickly grasp what’s new and improved.
What accessibility fixes does Safari Technology Preview 243 include?
The update resolves several issues that improve the experience for users relying on assistive technologies. Previously, the contextmenu event failed to trigger for elements inside iframes when activated via keyboard or VoiceOver (e.g., VO+Shift+M). This has now been fixed. Color picker inputs were also inaccessible to VoiceOver’s press action—that's corrected. Additionally, aria-hidden="true" was not properly invalidated when focus entered a hidden subtree; this bug is resolved. Support for base <select> elements was enhanced: the popover now closes upon selection, and the accessibility path placement remains accurate even when CSS transforms are applied. These changes make the browser more inclusive for keyboard and VoiceOver users.
How does this release address CSS animation conflicts?
Two key animation issues were fixed. First, when CSS transitions and animations both targeted the same property, !important declarations were not properly overriding animation values. This could lead to unexpected styling as the animation took precedence incorrectly. That behavior is now corrected. Second, an error in identity matrix decomposition was generating invalid quaternions, which caused transform animations to look wrong—for example, rotations or scales might appear distorted. The fix ensures that transform matrices decompose into valid quaternions, restoring accurate animation rendering. These improvements help developers reliably combine transitions, animations, and !important rules.
What new CSS features are included in this preview?
Two notable CSS additions arrive. The contain: style property now applies to CSS quote counters, as specified in CSS Containment Level 2. This allows developers to limit the scope of style containment, which can improve performance on complex pages by isolating quote counter increments. Additionally, the text-autospace property gains the insert keyword. This feature controls automatic spacing between characters in different scripts (e.g., Latin and CJK), and the new keyword inserts spacing where appropriate. These enhancements give web developers finer control over layout and typography.
Which layout and rendering bugs were fixed?
A long list of rendering issues were resolved. Flexbox now uses the actual flex-basis value (instead of the specified one) to determine definite sizes, fixing alignment quirks. Element positioning was incorrect when the containing block was an anonymous block—that's fixed. box-shadow now works on display: table-row elements. text-indent with calc() that includes percentages correctly treats percentage components as zero for intrinsic size contributions. Out-of-flow content set to fit-content now has the correct height. Percentage size resolution in flex items within quirks mode also works properly. clip-path: inset() with border-radius now renders accurately at various sizes. Additionally, the emulation of -webkit-box flexbox inside <fieldset> elements now sizes children correctly. Table elements with borders and certain combos of position: absolute and aspect-ratio: 1 also render correctly.
How does this update improve performance and selector handling?
The release includes a performance optimization for pages using :where and :is pseudo-class selectors. These selectors can sometimes cause performance bottlenecks, especially when used extensively with complex rules. The fix reduces the overhead, making such pages faster to process and render. This is part of ongoing work to ensure modern CSS features don't degrade browsing speed. Developers can use these selectors more freely knowing performance is improved.
How do I install or update to Safari Technology Preview 243?
If you already have Safari Technology Preview installed on macOS Tahoe or Sequoia, updating is simple: open System Settings, go to General, then Software Update. The new version will appear there. Alternatively, you can download the full installer from Apple’s developer website. This release incorporates WebKit changes from revisions 310600 through 312007, so it includes many under-the-hood improvements beyond those listed here.
Are there any other notable changes in this preview?
Yes, additional accessibility fixes include improved VoiceOver support for base <select> elements—specifically closing the popover upon selection and correcting the accessibility path positioning when CSS transforms are present. Also, the invalid aria-hidden invalidation issue when focus lands inside the aria-hidden subtree has been resolved, which helps screen readers maintain correct state. These, along with the CSS and animation fixes, make Safari Technology Preview 243 a substantial update for developers testing upcoming WebKit features.