Safari Technology Preview 250: three new CSS properties, and a deprecation that will break stylesheets

Safari Technology Preview 250 is available for macOS Golden Gate and macOS Tahoe, and it lands five entries under CSS new features along with a VoiceOver fix, four layout and paint fixes, and one deprecation ^[1][3]. It also fixes an IndexedDB bug that could leave an object store holding neither the old record nor the new one, which is the kind of defect that outranks any new property ^[16].

Count the CSS additions honestly: three are actually new properties. `text-decoration-inset`, `white-space-trim` and `wrap-inside` are new ^[5][6][7]. `content` on `::marker` is new support for an existing property on a pseudo-element, which is what lets you set list marker text from CSS ^[4]. `ruby-overhang` gains a `spaces` value that limits annotation overhang to adjacent spaces and punctuation, with `none` now an alias for it ^[8][9]. That is a behaviour change for anyone who already wrote `ruby-overhang: none`, not a new capability.

The planning caveat is structural, not editorial: the notes identify this build by a WebKit commit range, 317507@main to 317934@main, and say nothing about which shipping Safari release carries any of it ^[2]. Technology Preview is where you write the test page, not where you drop the fallback.

The paint fixes are the sort of thing teams have been working around for years. A `list-style-position: inside` marker glyph was being painted one device pixel away from the equivalent inline text ^[10]. `text-decoration` on `::selection` was never painted at all, and a second fix covers the case where the selected text had no decoration of its own ^[11][12]. A `max-content` sized block was collapsing to zero width when its child used an orthogonal writing mode ^[13].

The deprecation is the one item here that can break a production stylesheet: support for the non-standard `text` color value is removed, and WebKit points to `canvastext` ^[14]. Grep for it.

On accessibility, VoiceOver was reading a stray newline and skipping lines when navigating a `<textarea>` whose value ends in a line break ^[15]. Scrolling gets four fixes: `scrollIntoView()` on an inline element sharing a line with a much taller element was scrolling to the top of the line box rather than the element; Page Down and the spacebar were skipping intermediate scroll snap points; re-snapping after layout always preferred a focused element instead of only when focus changed; and a crash during window tear-down is gone ^{[17][18][19][20]}.

Elsewhere, `fetch()` gets initial support for uploading a `ReadableStream` body, along with the `duplex` option on `Request` that such uploads require ^[21][22]. JavaScript picks up the Explicit Resource Management proposal, including `using` and `await using`, `Symbol.dispose`, `DisposableStack` and `AsyncDisposableStack`, plus `Iterator.zip()` and `Iterator.zipKeyed()` ^[23][24]. WebAssembly gains relaxed SIMD instructions and multiple memories in a single module, and Web Inspector will now show WebAssembly modules in the Sources tab ^[25][26][27]. The Clipboard API can copy and paste `image/svg+xml`, sanitized on both read and write ^[28].