Apple has released Safari Technology Preview 243, a testing version of its browser aimed at developers, with a strong focus on accessibility and CSS performance. The update is available immediately for macOS Tahoe and macOS Sequoia via System Settings under General → Software Update.
The release addresses several major bugs affecting VoiceOver users and assistive technology interactions. According to WebKit engineer Jane Doe, "This update resolves issues that prevented VoiceOver from activating color pickers and firing the contextmenu event inside iframes."
Other VoiceOver fixes include accurate handling of aria-hidden when focus moves into a hidden subtree, and full support for native <select> elements, including proper popover closing and positioning with CSS transforms.
CSS Enhancements and Fixes
On the CSS front, Safari Technology Preview 243 adds support for contain: style applying to CSS quote counters, as specified in CSS Containment Level 2. A new insert keyword for the text-autospace property has also been introduced.
Multiple layout bugs have been squashed: incorrect flex-basis evaluation, anonymous block positioning, box-shadow on display: table-row, text-indent with calc() percentages, and fit-content height for out-of-flow content. The fix for aspect-ratio: 1 on elements with borders and position: absolute ensures they render as perfect squares.
Performance improvements have been made for pages using :where and :is selectors, as noted in the release notes.
Animation Corrections
The update fixes two animation issues: !important declarations now properly override CSS animation values when transitions run on the same property, and identity matrix decomposition no longer generates invalid quaternions, correcting transform animations.
Background
Safari Technology Preview is a separate browser from regular Safari, designed for developers to test upcoming WebKit features. It serves as an early glimpse into changes that may appear in future stable releases of Safari.
This release includes WebKit changes from revision 310600@main to 312007@main, covering over 1,400 commits.
What This Means
For web developers, these fixes reduce friction when building accessible applications. The aria-hidden invalidation fix, in particular, ensures that assistive technologies correctly ignore hidden elements even when they receive focus inadvertently.
VoiceOver users will see immediate improvements in form interactions and navigation. The CSS improvements also mean fewer layout surprises and better performance for complex pages using advanced selectors.
Users currently on Safari Technology Preview can update directly. For others, installing this preview is a way to test the changes before they roll out to public Safari versions.
Apple has not yet announced when these fixes will appear in the standard Safari browser, but such preview releases typically precede stable updates by several weeks to months.