Chrome 159 Release Notes

AccentColor and AccentColorText reflect the element's effective accent-color value instead of only platform-provided system accent colors.

This allows CSS to reference the same colors used by accent-color styling, making it easier to keep custom styling consistent with form controls and other accented UI. It aligns Chromium's behavior with the CSS Color Module Level 4 specification.

Makes the computed value of the background-* longhands keep the number of comma-separated values the author specified, instead of repeating or truncating it to the background-image layer count. Repeating and truncating are used-value behavior: "The computed values of the coordinating list properties are not affected by such truncation or repetition." This feature implements the behavior defined in the https://drafts.csswg.org/css-values-4/ Appendix A.

Implements the CSS corner shorthand and per-corner sub-shorthands (corner-top-left, corner-top-right, corner-bottom-left, corner-bottom-right) as well as physical (corner-top, corner-bottom) and logical (corner-block-start, corner-block-end, etc.) edge shorthands. These allow setting both border-radius and corner-shape for individual corners in a single declaration. Additionally, corners is retained as a compat alias for the corner shorthand.

sampler: https://static.januschka.com/i-425897047/

CL: https://chromium-review.googlesource.com/c/chromium/src/+/7747994

Returns null from CSSImportRule.styleSheet when an @import rule has no associated stylesheet, including when its supports() condition is false. This lets developers check whether a stylesheet is associated with the rule before accessing its properties.

Allows authors to omit any descriptor in an @property rule and the corresponding optional members of CSS.registerProperty(). Omitted values default to universal syntax, inheritance, and the guaranteed-invalid initial value; invalid descriptors use normal CSS fallback behavior.

This feature lets a single-axis scroll container (for example, one with overflow: auto clip) handle scroll snap area propagation and alignment separately for each axis.

Single-axis scroll containers are now supported (https://chromestatus.com/feature/5067363861004288). Without this feature, such a container captures a snap area on both axes, even the axis it can't scroll. The snap area then can't align on that axis.

With this feature, if a snap area sets alignment on both axes, the single-axis container handles only the axis it scrolls. The other axis goes up to the nearest ancestor scroll container that scrolls in that direction.

https://github.com/whatwg/html/pull/12898

Sanitizer API also sanitizes javascript:-URLs, when they are used for navigation. This was originally done as a side effect of any "safe" method that uses Sanitizer, and omittted for any "unsafe" method. The HTML standard recently regularized this and made this a developer-selectable option, instead of a side-effect of a particular method.

Behaviour when the option is not used remains the same.

Prerenders cross-origin iframes with an opt-in response header.

Browsers will now prerender all cross-origin frames if the top-level frame's HTTP response includes the Supports-Loading-Mode: prerender-cross-origin-frames.

The Web Speech API currently does not expose the acoustic timing bounds of recognized speech segments, making it difficult to associate transcribed text with media timelines or generate synchronized subtitle cues. We propose adding speechStartTime and speechEndTime (double, in seconds relative to stream start) attributes on the SpeechRecognitionResult interface.

Expand the TextMetrics Canvas API to support selection rectangles, bounding box queries, and glyph cluster-based operations.

This new functionality should enable complex text editing applications with accurate selection, caret positioning, and hit testing. Additionally, cluster-based rendering facilitates sophisticated text effects such as independent character animations and styling.

Updates navigator.mediaSession.setMicrophoneActive() and navigator.mediaSession.setCameraActive() to return a Promise<undefined> instead of undefined, matching the W3C Media Session specification. In a fully active document, the returned promise resolves with undefined; if the associated document is not fully active, it returns a promise rejected with an InvalidStateError DOMException.

Exposes a shared MessagePort on AudioWorklet and AudioWorkletGlobalScope. This lets web applications communicate directly between the main thread AudioWorklet and the AudioWorkletGlobalScope without creating a bootstrap AudioWorkletProcessor only for message passing.

A TC39 proposal introducing \A, \z and \Z character escapes to Unicode-mode regular expressions as synonyms for (?-m:^), (?-m:$) and (?=(?:\r\n|\n|\r|\u2028|\u2029)?(?-m:$)), respectively.

Adds structured JavaScript access to SVG path data through three methods on SVGPathElement: getPathData() reads the path as an array of {type, values} objects containing each segment's command and numeric parameters. setPathData() updates the path from such an array, getPathSegmentAtLength() returns the segment at a specified distance along the path. These methods let developers inspect, edit, and construct paths without manually parsing or serializing the d attribute.

The optional getPathData({normalize: true}) setting simplifies path data to absolute move, line, cubic Bézier, and close commands (M, L, C, and Z). All three APIs operate on the base value of the d attribute, not CSS-computed or animated values.

Adds the  WebTransportOptions.datagramsReadableType  constructor option. By default, incoming WebTransport Datagrams are exposed through a default  ReadableStream . Applications that require BYOB reading can request a readable byte stream by setting  datagramsReadableType: "bytes" .

Adds the modern WebTransport Datagram sending API.

WebTransportDatagramDuplexStream.createWritable() creates independent WebTransportDatagramsWritable streams. Each writable has mutable sendGroup and sendOrder attributes for expressing relative priority among queued WebTransport data in the same send group. Chromium currently applies this ordering among Datagram writables.

The implementation also reports the negotiated maximum outgoing Datagram payload size and discards oversized writes as required by the WebTransport specification.

Adds the congestionControl constructor option and read-only attribute to WebTransport. Applications can request "default", "throughput", or "low-latency" behavior, allowing the user agent to select suitable congestion-control behavior for each session.

WebTransport.getStats() provides asynchronous statistics for an existing connection: round-trip time measurements when available, an estimated sending rate when available, and counts of expired, lost, and dropped datagrams. Statistics remain accessible after the connection closes. Chromium does not currently expose connection byte or packet totals.

Adds WebTransport.exportKeyingMaterial(), which allows an application to derive cryptographic keying material bound to an established WebTransport session.

The method accepts application provided binary label and context values and a requested output length and returns a Promise<Uint8Array>. Chromium supports label and context values up to 255 bytes and output lengths from 1 through 4096 bytes.

For WebTransport over HTTP/3, Chromium includes the WebTransport CONNECT stream ID in the TLS exporter context. This ensures that separate WebTransport sessions derive different keying material even when they share the same underlying HTTP/3 connection.

Adds the standardized WebTransportReceiveStream interface, a ReadableStream subclass used for incoming unidirectional streams and the readable side of bidirectional streams. Its getStats() method returns per-stream byte counters: bytesReceived reports bytes received from the network, while bytesRead reports bytes delivered to the application.

WebTransport already lets sites send data through WritableStreams. This feature lets applications assign outgoing streams to send groups and use sendOrder to prioritize streams within each group. It also provides sending statistics for streams and groups while preserving WritableStream transfer behavior.

Updates Chromium WebTransportError to match the current WebTransport specification. Adds the standard (message, options) constructor while preserving the shipped dictionary constructor for compatibility; carries the full unsigned-long stream error code end to end; and makes WebTransportError structured-clonable while preserving its message, source, and nullable error code. Serialization is enabled by default behind a writer-side runtime kill switch, while decoding remains permanently enabled for persisted values.