Release Notes for Safari Technology Preview 127

Safari Technology Preview Release 127 is now available for download 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.

Note: Tab Groups and Theme Colors are not available in this release on macOS Big Sur.


  • Added discrete animation support for grid-template-columns and grid-template-rows (r278173)
  • Added support for calc() on components inside relative color syntax colors (r278261, r278304)
  • Added support for “relative color syntax” for color() (r278364)
  • Added additional target luminance keywords for color-contrast() (r278262)
  • Fixed the height of an empty table inside an orthogonal flex parent (r277777)
  • Fixed will-change: position to only create a containing block for position: absolute elements (r277579)
  • Made will-change: transform-style create a containing block (r277566)
  • Fixed percent calculations for padding-top and padding-bottom when the parent has padding (r278194)


  • Fixed scroll snapping in non-horizontal writing modes (r278350)
  • Fixed layout issue handling changes to scroll-snap properties (r278193)
  • Improved scrolling performance when background-attachment: fixed is used inside a position: fixed layer (r278419)
  • Improved how the current document scroll position is maintained on full page zoom (r277775)


  • Added support for Ergonomic Brand Checks proposal (e.g. #x in object) behind the--usePrivateIn flag (r277926)
  • Fixed private static method in class-scope (r278510)
  • Optimized Function.prototype.toString (r278462)
  • Optimized in with non-identifier via non ad-hoc IC (r278445)


  • Added MediaSession.callActionHandler (r278222)
  • Fixed MediaSession action handlers to be treated as having a user gesture (r277588)
  • Fixed macOS WebM Format Reader returning enabled for tracks that do not have samples (r278155)
  • Added support for H.264 profiles in MediaRecorder (r278158)


  • Changed to tighter bitrate allocation rules for WebRTC H.264 software encoder (r278272)


  • Added support for creating, accessing, and setting non-sRGB ImageData via canvas (r277569)
  • Added support for dispatching wheel events with ctrlKey on pinch gestures, which is commonly used for zooming embedded maps (r277772)
  • Fixed the value of a color input to update visually when using setAttribute (r277778)


  • Fixed increased contrast not detected in the browser until an additional setting is applied (r277971)
  • Fixed accessibility caption styles to always reflect the selection (r277874)


  • Enabled <summary> to be a flex container (r278280)
  • Changed grid track size to reject a unit-less length (r277868)
  • Fixed incorrect selection when a tall float element is present (r278379)
  • Fixed incorrect text selection when crossing a flex item boundary (r278411)