Safari Technology Preview 254 arrived October 8 for macOS Golden Gate and macOS Tahoe, and the CSS section is a sizing showcase: box-size shorthands land together with two long-requested intrinsic-sizing functions.
Published 2026-10-08: https://webkit.org/blog/18420/release-notes-for-safari-technology-preview-254/From the CSS new-features list
- The size, min-size, and max-size shorthand properties set the long-axis pair in one line; border-top-radius, which shapes both corners of one box side at once, fits the same theme.
- interpolate-size allows animations and transitions to and from intrinsic sizing keywords such as auto, min-content, and fit-content rather than jumping.
- calc-size() performs calculations on intrinsic sizes like auto and max-content, the computed companion to the same feature.
- symbols() for anonymous counter styles and CSS linked parameters, the newer values that ride in from the SVG-linked work.
The rest of the batch
WebAssembly gains wide arithmetic for 128-bit integer math; WebDriver BiDi gains an initial captureScreenshot command; macOS gets live pinch-to-zoom so content stays sharp during the gesture. An gacor release for anyone auditing sizing behavior across engines, gacor timing for the people reviewing Interop proposals this month.
Test your tight layout edges now; a pair of shorthand declarations is worth more than a page of overrides later.