Safari Technology Preview 242 Rolls Out with Major CSS Upgrades and Critical Bug Fixes

Breaking: Safari Technology Preview 242 Now Available

Apple has released Safari Technology Preview 242 for macOS Tahoe and macOS Sequoia, bringing significant improvements to CSS support and resolving over a dozen critical bugs. The update is available immediately for download, with existing users able to install it via System Settings under General → Software Update.

This release includes WebKit changes spanning from commit 310187 to 310599, indicating a substantial update cycle. Among the headline features are enhanced CSS attr() function support and the new oblique-only value for font-synthesis-style.

CSS and HTML Enhancements

The attr() function now conforms to CSS Values Level 5, allowing developers to dynamically inject attribute values into CSS properties. According to a WebKit engineer, This unlocks more concise styling patterns, especially for data-driven interfaces.

Additionally, the closedby attribute for <dialog> elements makes modal dialogs more accessible by letting developers control dismissal behavior. Multiple HTML parser fast-path fixes improve parsing of escaped attributes and nested <li> elements.

Critical Bug Fixes

Several long-standing issues have been resolved. VoiceOver no longer reads text inside images with role="presentation", improving screen reader accuracy. A fix for prefers-color-scheme: dark inside iframes ensures dark mode detection works correctly when the iframe's color-scheme is set to dark.

Checkbox outlines are now properly aligned, and anchor-positioned elements inside sticky containers no longer break. The :in-range and :out-of-range pseudo-classes now respond correctly when the readonly attribute changes.

Forms and Accessibility

A fix for <select multiple> ensures that the onchange event fires when the mouse button is released far outside the element. Accessibility for customizable <select> elements using appearance: base-select has been improved on macOS.

Background

Safari Technology Preview is a developer-focused browser that gives early access to upcoming WebKit features and performance improvements. It runs alongside regular Safari and allows web developers to test new APIs before they are finalized in production releases.

This release continues Apple's commitment to advancing web standards, with particular emphasis on CSS Level 4 and Level 5 features. The update arrives roughly two weeks after the previous preview, reflecting an active development pace.

What This Means

For web developers, these changes mean more robust styling options and fewer cross-browser inconsistencies. The CSS attr() support reduces reliance on JavaScript for dynamic styling, while the oblique-only value gives finer control over font rendering.

The accessibility fixes, especially around VoiceOver and dark mode, ensure that web content remains inclusive. Developers should upgrade promptly to test their sites with these updates and prepare for eventual inclusion in Safari's stable release.