# Safari Technology Preview 127 Release Notes Preview the latest web technology updates including: CSS, Scrolling, JavaScript, Media, WebRTC, Web API, Accessibility, and Rendering. ## Overview [Safari Technology Preview](https://webkit.org/blog/6017/introducing-safari-technology-preview/) Release 127 is now [available for download](https://webkit.org/downloads/) for macOS Big Sur and betas of macOS Monterey. If you already have Safari Technology Preview installed, you can update in the Software Update pane of System Preferences on macOS. This release covers WebKit revisions [277448-278571](https://trac.webkit.org/log?stop_rev=277448&rev=278571&limit=999). **Note:** Tab Groups and Theme Colors are not available in this release on macOS Big Sur. ### CSS - Added discrete animation support for `grid-template-columns` and `grid-template-rows` ([r278173](https://trac.webkit.org/changeset/278173/webkit/)) - Added support for `calc()` on components inside relative color syntax colors ([r278261](https://trac.webkit.org/changeset/278261/webkit/), [r278304](https://trac.webkit.org/changeset/278304/webkit/)) - Added support for “relative color syntax” for `color()` ([r278364](https://trac.webkit.org/changeset/278364/webkit/)) - Added additional target luminance keywords for `color-contrast()` ([r278262](https://trac.webkit.org/changeset/278262/webkit/)) - Fixed the height of an empty table inside an orthogonal flex parent ([r277777](https://trac.webkit.org/changeset/277777/webkit/)) - Fixed `will-change: position` to only create a containing block for `position: absolute` elements ([r277579](https://trac.webkit.org/changeset/277579/webkit/)) - Made `will-change: transform-style` create a containing block ([r277566](https://trac.webkit.org/changeset/277566/webkit/)) - Fixed percent calculations for `padding-top` and `padding-bottom` when the parent has padding ([r278194](https://trac.webkit.org/changeset/278194/webkit/)) ### Scrolling - Fixed scroll snapping in non-horizontal writing modes ([r278350](https://trac.webkit.org/changeset/278350/webkit/)) - Fixed layout issue handling changes to `scroll-snap` properties ([r278193](https://trac.webkit.org/changeset/278193/webkit/)) - Improved scrolling performance when `background-attachment: fixed` is used inside a `position: fixed` layer ([r278419](https://trac.webkit.org/changeset/278419/webkit/)) - Improved how the current document scroll position is maintained on full page zoom ([r277775](https://trac.webkit.org/changeset/277775/webkit/)) ### JavaScript - Added support for Ergonomic Brand Checks proposal (e.g. `#x in object`) behind the`--usePrivateIn` flag ([r277926](https://trac.webkit.org/changeset/277926/webkit/)) - Fixed private static method in class-scope ([r278510](https://trac.webkit.org/changeset/278510/webkit/)) - Optimized `Function.prototype.toString` ([r278462](https://trac.webkit.org/changeset/278462/webkit/)) - Optimized `in` with non-identifier via non ad-hoc IC ([r278445](https://trac.webkit.org/changeset/278445/webkit/)) ### Media - Added `MediaSession.callActionHandler` ([r278222](https://trac.webkit.org/changeset/278222/webkit/)) - Fixed MediaSession action handlers to be treated as having a user gesture ([r277588](https://trac.webkit.org/changeset/277588/webkit/)) - Fixed macOS WebM Format Reader returning enabled for tracks that do not have samples ([r278155](https://trac.webkit.org/changeset/278155/webkit/)) - Added support for H.264 profiles in MediaRecorder ([r278158](https://trac.webkit.org/changeset/278158/webkit/)) ### WebRTC - Changed to tighter bitrate allocation rules for WebRTC H.264 software encoder ([r278272](https://trac.webkit.org/changeset/278272/webkit/)) ### Web API - Added support for creating, accessing, and setting non-sRGB ImageData via canvas ([r277569](https://trac.webkit.org/changeset/277569/webkit/)) - Added support for dispatching `wheel` events with `ctrlKey` on pinch gestures, which is commonly used for zooming embedded maps ([r277772](https://trac.webkit.org/changeset/277772/webkit/)) - Fixed the value of a color input to update visually when using `setAttribute` ([r277778](https://trac.webkit.org/changeset/277778/webkit/)) ### Accessibility - Fixed increased contrast not detected in the browser until an additional setting is applied ([r277971](https://trac.webkit.org/changeset/277971/webkit/)) - Fixed accessibility caption styles to always reflect the selection ([r277874](https://trac.webkit.org/changeset/277874/webkit/)) ### Rendering - Enabled `

` to be a flex container ([r278280](https://trac.webkit.org/changeset/278280/webkit/)) - Changed grid track size to reject a unit-less length ([r277868](https://trac.webkit.org/changeset/277868/webkit/)) - Fixed incorrect selection when a tall float element is present ([r278379](https://trac.webkit.org/changeset/278379/webkit/)) - Fixed incorrect text selection when crossing a flex item boundary ([r278411](https://trac.webkit.org/changeset/278411/webkit/)) --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)