Apple has just released Safari Technology Preview 243, bringing a fresh set of WebKit refinements for macOS Tahoe and macOS Sequoia. Whether you're a web developer or an accessibility advocate, this update touches on everything from VoiceOver interactions to CSS layout quirks. Already have the preview installed? You can update via System Settings > General > Software Update. Let's dive into the ten most significant changes—from bug fixes to new capabilities—that make this release a must-try for anyone pushing the web forward.
1. Accessibility Wins for VoiceOver and Keyboard Users
This release tackles several accessibility pain points. First, the contextmenu event now fires correctly inside iframes when triggered via keyboard or assistive technology like VoiceOver’s VO+Shift+M—a crucial fix for right-click menus. Color picker inputs can now be activated using VoiceOver’s press action, making form interactions smoother. Additionally, aria-hidden="true" is properly invalidated when focus lands inside a hidden subtree, ensuring screen readers don't miss dynamic content. Finally, base <select> elements get better VoiceOver support, including proper popover dismissal on selection and corrected accessibility path positioning even when CSS transforms are applied.
2. Animation Stability: No More Wrong Interpolations
Two animation bugs have been squashed. The first resolves an issue where !important declarations were being ignored when both CSS animations and transitions targeted the same property—now cascade priority is respected. The second fix corrects identity matrix decomposition that was generating invalid quaternions, which led to skewed transform animations. Developers can expect more predictable motion effects, especially in complex 3D scenarios.
3. New CSS Containment for Quote Counters
Following the CSS Containment Level 2 spec, Safari now supports contain: style applying to CSS quote counters. This means you can isolate quote-related styles within a subtree, improving performance and predictability when using content: open-quote or counter-increment. It’s a subtle but powerful addition for large documents with extensive quoting logic.
4. Text-Autospace Gets an Insert Keyword
Text spacing control gets an upgrade with the insert keyword for the text-autospace property. This allows developers to fine-tune how auto-spacing behaves when inserting content—useful for East Asian typography or any scenario where automatic spacing needs manual overrides.
5. Flexbox Fixes: Better Basis and Percentage Sizing
Several flex layout issues have been addressed. The layout engine now uses the used flex-basis instead of the specified value for definiteness evaluation, aligning with the spec. Additionally, percentage size resolution in flex items works correctly in quirks mode, and -webkit-box emulation now sizes children properly inside <fieldset> elements. These changes eliminate many edge-case layout breaks.
6. Box-Shadow Works on Table-Row Elements
A long-standing annoyance is fixed: box-shadow now renders correctly on display: table-row elements. Previously, it had no effect, forcing developers to wrap rows in extra containers. This change simplifies table styling and opens up new creative possibilities.
7. Text-Indent Percentages in Calc() Are Now Consistent
When using text-indent with calc() containing percentages, those percentages are now treated as zero for intrinsic size contributions. This prevents unintended horizontal scrolling or misalignment in fluid layouts, especially when indenting inline content within responsive containers.
8. Clip-Path Inset Border-Radius Renders Correctly
Rounding issues with clip-path: inset() and border-radius have been resolved. At certain element and clip-path sizes, the corners would appear jagged or incorrectly clipped. Now the clipping respects border-radius values accurately, making it easier to create polished, rounded visual effects.
9. Performance Boost for :where and :is Selectors
Pages using modern CSS pseudo-classes like :where and :is will see improved performance. The fix optimizes how these selectors are evaluated, reducing style recalculation time on complex stylesheets—especially beneficial for large component libraries or heavy use of selector lists.
10. Miscellaneous Layout Quandaries Resolved
Rounding out the update are several smaller but important fixes: element positioning when the containing block is an anonymous block, out-of-flow content with fit-content height, incorrect layout for display: table elements with borders, and ensuring elements with border, position: absolute, and aspect-ratio: 1 render as perfect squares. Each fix reduces the need for hacky workarounds in modern web design.
Whether you're building accessible interfaces or fine-tuning CSS animations, Safari Technology Preview 243 delivers tangible improvements. Download or update today and test your projects against these fixes—your users will thank you for it.