# Safari Technology Preview 158 Release Notes Preview the latest web technology updates including: Web Inspector, CSS, Rendering, Media, JavaScript, WebCodecs, and Web API. ## Overview [Safari Technology Preview](https://webkit.org/blog/6017/introducing-safari-technology-preview/) Release 158 is now [available for download](https://webkit.org/downloads/) for macOS Monterey 12.3 or later and macOS Ventura. If you already have Safari Technology Preview installed, you can update in the Software Update pane of System Preferences on macOS Monterey, or System Settings under General → Software Update on macOS Ventura. This release includes WebKit changes between: [255892@main…256138@main](https://github.com/WebKit/WebKit/compare/0acf2457faa716438f87f4446a13b3da6a35be0f...c4da39ca9400b440d2d14664731fe2b2ed4c45f4) **Note:** Shared Tab Groups and syncing for Tab Groups, Website Settings, and Web Extensions are not enabled in this release. ### Web Inspector - Added support for editing @-rules in the Styles sidebar of the Elements tab ([256043@main](https://commits.webkit.org/256043@main)) ### CSS - Implemented CSS `font-size-adjust` property ([255927@main](https://commits.webkit.org/255927@main)) - Implemented `font-variant-alternates` functions, along with matching `@font-feature-values` at-rule ([256002@main](https://commits.webkit.org/256002@main), [255677@main](https://commits.webkit.org/255677@main)) - Implemented CSS property `contain-intrinsic-size` behind a flag ([255971@main](https://commits.webkit.org/255971@main)) - Changed to allow `calc()` with combined percentages and lengths for `line-height` ([256095@main](https://commits.webkit.org/256095@main)) - Changed to always use percentages for computed values of `font-stretch`, never keywords ([256094@main](https://commits.webkit.org/256094@main)) - Fixed `font` shorthand to not reject values that happen to have CSS-wide keywords as non-first identifiers in a font family name ([255894@main](https://commits.webkit.org/255894@main)) - Fixed `font-style` descriptor for `@font-face` to accept angle ranges in reverse order ([255893@main](https://commits.webkit.org/255893@main)) - Fixed `font-style: oblique` with `calc()` to allow out-of-range angles and clamp them for computed style ([255925@main](https://commits.webkit.org/255925@main)) - Fixed computed value CSS gradients to serialize colors in their computed form ([256073@main](https://commits.webkit.org/256073@main)) - Fixed `text-shadow` positioning on text with `text-combine-upright` ([255892@main](https://commits.webkit.org/255892@main)) - Fixed `line-height` to allow `calc()` with combined percentages and lengths ([256095@main](https://commits.webkit.org/256095@main)) ### Rendering - Changed to check for overflow content after trimming trailing content ([256045@main](https://commits.webkit.org/256045@main)) - Fixed a table cell overflowing its contents when it has inline children that change the writing-mode ([255919@main](https://commits.webkit.org/255919@main)) - Fixed elements with negative margins to not avoid floats when appropriate ([256132@main](https://commits.webkit.org/256132@main)) ### Media - Enabled AVIF image decoding for macOS Monterey and macOS Big Sur ([255984@main](https://commits.webkit.org/255984@main)) - Fixed “A MediaStreamTrack ended due to a capture failure” when selecting bluetooth headphones as audio input device ([256091@main](https://commits.webkit.org/256091@main)) ### JavaScript - Accelerated `Array.prototype.slice` on DirectArguments ([256027@main](https://commits.webkit.org/256027@main)) - Accelerated `Array.prototype.concat` when applied to the self array ([256040@main](https://commits.webkit.org/256040@main)) ### WebCodecs - Enabled WebCodecs by default ([256060@main](https://commits.webkit.org/256060@main)) - Added WebCodecsVideoFrame initial support for serialisation and transfer ([255949@main](https://commits.webkit.org/255949@main)) - Changed to schedule dequeue event when the encoder queue size decreases ([255962@main](https://commits.webkit.org/255962@main)) - Changed to set VPx decoder frame type based on given parameter ([255963@main](https://commits.webkit.org/255963@main)) - Changed to prevent garbage collecting an encoder or decoder with content being processed ([256007@main](https://commits.webkit.org/256007@main)) - Exposed decoded video frames colorSpace ([256068@main](https://commits.webkit.org/256068@main)) - Exposed encoder color space in decoder config ([256052@main](https://commits.webkit.org/256052@main)) - Flushed before reconfiguring the encoder ([255957@main](https://commits.webkit.org/255957@main)) - Implemented pixel buffer conversion for video frames produced by libwebrtc VPX decoders ([255958@main](https://commits.webkit.org/255958@main)) ### Web API - Aligned fetch header handling with fetch specification ([256003@main](https://commits.webkit.org/256003@main)) - Changed calling `CSSStyleValue.parseAll()` on a list-valued CSS property to split its value list ([256070@main](https://commits.webkit.org/256070@main)) - Changed `CSSStyleValue.parse()` to throw when passed an empty string as custom property value ([256011@main](https://commits.webkit.org/256011@main)) - Changed creating a shared worker connection to retry without providing a specific webprocess ([255968@main](https://commits.webkit.org/255968@main)) - Implemented input validation for CSSRGB constructor and setters ([256024@main](https://commits.webkit.org/256024@main)) - Optimized `postMessage` between two MessageChannel ports living in the same process ([255948@main](https://commits.webkit.org/255948@main)) --- Copyright © 2026 Apple Inc. 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