Safari Technology Preview 243 is now available for download on macOS Tahoe and macOS Sequoia. If you already have it installed, you can update via System Settings > General > Software Update. This release includes a range of WebKit improvements, from accessibility enhancements to CSS and animation fixes. Below, we answer your most pressing questions about what's changed.
What is Safari Technology Preview 243 and how can I install or update it?
Safari Technology Preview is an experimental version of Safari that lets developers test upcoming web technologies. Release 243 brings WebKit updates between builds 310600 and 312007. To get it, download the latest version from Apple's developer portal if you're on macOS Tahoe or macOS Sequoia. If you already have a previous Technology Preview installed, open System Settings → General → Software Update to trigger the update. The process is seamless, ensuring you're always on the cutting edge of web standards.
What accessibility issues were resolved in this release?
Several key accessibility bugs were fixed to improve assistive technology support. First, the contextmenu event now fires properly for elements inside iframes when triggered by keyboard or VoiceOver actions like VO+Shift+M. Color picker inputs can now be activated using VoiceOver's press action. The team also fixed invalidation of aria-hidden="true" when focus enters the hidden subtree, ensuring correct semantics in dynamic pages. Additionally, base <select> elements now close their popover on selection, and their accessibility path positioning works correctly even with CSS transforms. These changes make the browser more inclusive for users relying on screen readers.
What animation-related bugs were fixed?
Two important animation issues were addressed. One bug caused !important declarations to be ignored when both CSS animations and transitions ran on the same property—now fixed so !important takes precedence as expected. Another fix resolved incorrect quaternion generation during identity matrix decomposition, which led to wonky transform animations. Developers relying on complex transforms and transitions will see more predictable behavior.
What new CSS features were added?
This release adds two CSS enhancements. First, support for contain: style now applies to CSS quote counters, as specified in CSS Containment Level 2. This improves performance by limiting style calculations for sections of the page. Second, the insert keyword for the text-autospace property has been added, offering finer control over spacing around inserted characters. These additions give developers more power to optimize layout and typography.
What CSS layout and rendering issues were fixed?
Numerous layout bugs were squashed. Flexbox now uses the used flex-basis rather than the specified value for definiteness evaluation, fixing sizing inconsistencies. Element positioning inside anonymous block containers works correctly again. Box-shadow applies properly to display: table-row elements. The text-indent property with calc() percentages no longer miscounts intrinsic sizes. Out-of-flow content with fit-content height now renders at the right height. Percentage size resolution in flex items under quirks mode is fixed. The clip-path: inset() with border-radius now renders correctly at various sizes. -webkit-box flexbox emulation inside <fieldset> sizes children properly. Table display with borders no longer causes incorrect layout. And elements with border, position: absolute, and aspect-ratio: 1 now render as squares.
Were there any performance improvements for CSS selectors?
Yes, the team improved performance on pages using :where and :is pseudo-class selectors. These modern selectors are popular for writing simpler and more maintainable CSS, but they could be slower in complex stylesheets. This update optimizes their matching logic, making them snappier without altering behavior. Developers should notice faster rendering on sites that heavily use these selectors, especially when combined with large DOM trees. No other selector-related changes were mentioned.
How did this release improve handling of CSS containment and text-autospace?
As noted in the new features section, this release adds support for contain: style applying to CSS quote counters, which is part of the CSS Containment Level 2 specification. This helps browsers optimize style recalculations by containing the scope of quotes. Separately, the insert keyword for text-autospace gives developers a way to control automatic spacing around inserted content, like when using the insert value in the text-autospace property (which manages spacing between ideographic and non-ideographic characters). Both additions are subtle but powerful tools for advanced CSS authors.