Apple has released Safari Technology Preview 240, the latest experimental build for macOS Tahoe and macOS Sequoia. This version brings important WebKit improvements that affect CSS, editing, forms, HTML parsing, and media handling. Whether you're a web developer or an early adopter, these ten updates are essential for understanding what's new. If you already have the preview installed, update via System Settings > General > Software Update. Let's dive into the changes.
1. New CSS revert-rule Keyword
The biggest CSS addition is the revert-rule keyword. This feature allows you to roll back the cascade for a specific style rule, effectively making the browser behave as if that rule never existed. It's a powerful tool for resetting styles in complex layouts, giving developers finer control over inheritance and specificity. This change originates from WebKit bug 308733.
2. Smoother Custom Scrollbars on macOS
Custom CSS scrollbars now display correctly without being cut off. Previously, the scrollbar corner rect was sized incorrectly, leading to visual glitches. This fix (bug 309119) ensures that your styled scrollbars render as intended across macOS, providing a more polished user experience.
3. Better Hanging Punctuation Support
Two fixes improve hanging punctuation. First, the apostrophe (U+0027) and quotation mark (U+0022) now hang properly when using the CSS property. Second, ideographic space (U+3000) is also supported as a hangable character when paired with the first value. These changes refine typographic control for international text.
4. Enhanced Editing: Font Picker & Emoji Copy-Paste
Editing gets two significant fixes. The Font Picker no longer becomes unusable after changing fonts in multi-line text (bug 308562). Additionally, emoji images are now preserved correctly when copying and pasting between different websites (bug 309176). This means richer, more reliable text editing in web apps.
5. Fixed Text Selection with Absolute Positioning
When selecting text inside an absolutely-positioned element nested within a user-select: none container, the selection no longer jumps unexpectedly (bug 308451). This fix stabilizes user interactions in complex document layouts, making content selection predictable.
6. Smarter Form Navigation: Tab Order Preserved
A frustrating form issue has been resolved: keyboard tabbing position is no longer lost when a focused button becomes disabled (bug 308991). Previously, the focus jumped to the page start; now it stays in the correct logical order, improving accessibility and form usability.
7. Stricter Viewport Meta Parsing
The viewport <meta> tag now correctly treats form feed as ASCII whitespace, aligning with the HTML specification (bug 309044). This change ensures consistent viewport behavior across all compliant browsers, reducing subtle rendering differences.
8. Corrected Margin Attributes for Body, Iframe, and Frame
Pixel-length margin attributes on <body>, <iframe>, and <frame> were previously parsed incorrectly (bug 308526). This fix aligns Safari with the HTML standard, ensuring that explicit margin values are applied as intended by developers.
9. Expanded Media Decoding: WebM, VP8, and Opus
Three media decoding issues are resolved. WebM audio files with more than two channels now decode successfully (bug 308749). MediaCapabilities.decodingInfo() correctly reports VP8 in WebM as supported (bug 308789). Additionally, MP4 files containing Opus audio tracks can be decoded using decodeAudioData (bug 309140), broadening audio format support.
10. Polished Media Playback: Live Text, FairPlay, Autoplay & More
Several playback improvements include: Live Text selection is now available on paused fullscreen videos (bug 308498); FairPlay-protected VP9 content plays via MediaSource (bug 308622); autoplay waits for default text tracks to load (bug 308796); the currentTime getter returns defaultPlaybackStartPosition when no player exists (bug 308654); proper timeupdate events fire during media load (bug 308695); and preload attribute handling is fixed. These changes make media playback more robust and standards-compliant.
Safari Technology Preview 240 continues WebKit's steady progress toward a faster, more reliable browsing experience. With these ten updates, developers can expect smoother CSS control, better editing tools, stricter HTML parsing, and expanded media support. Update today and test your projects against these changes to ensure compatibility.