Published: March 2, 2026

Welcome to the January 2026 edition of the Baseline digest. Each month, we highlight the web platform features that have reached new milestones in Baseline, helping you understand what tools are ready to use in your projects today.

January was an exciting start to the year, with several significant APIs and CSS units moving into the Newly available category, along with a major layout improvement becoming Widely available.

Baseline Newly available features

The following web features became Baseline Newly available in January 2026.

Active view transition

The :active-view-transition CSS pseudo-class is now Baseline Newly available. This selector allows developers to target and style the root element of a document specifically while a view transition is in progress. This is particularly useful for applying global styles or adjustments that should only exist during the transition period, such as changing the background color of the transition overlay or adjusting the z-index of specific layers to ensure a smooth visual flow.

JavaScript modules in service workers

Service workers now support JavaScript modules across all major browser engines. By setting the type: 'module' option when calling navigator.serviceWorker.register(), you can use standard import and export statements within your service worker script. This brings service workers in line with modern JavaScript development practices, allowing for better code organization, easier dependency management, and the ability to share code between the main thread and the background worker.

Navigation API

The Navigation API provides a modern, purpose-built alternative to the legacy History API, specifically designed for the needs of single-page applications (SPAs). It offers a centralized way to initiate, intercept, and manage all types of navigation actions, including those triggered by the browser's back and forward buttons. With events like Maps, developers can implement smoother client-side routing with less boilerplate code. For a deeper dive into how this changes the way we build for the web, check out our dedicated blog post: Modern client-side routing: the Navigation API.

rcap CSS unit

The rcap unit is a root-font-relative length unit equal to the "cap height" (the nominal height of capital letters) of the root element's font. This allows for precise typographic layouts that scale relative to the primary typeface used on the site, rather than just the font size.

rch CSS unit

Similar to the ch unit but relative to the root element, the rch unit represents the width—or more specifically, the advance measure—of the "0" (zero) glyph in the root element's font. It is ideal for creating layouts that depend on character width, such as a container that should precisely fit a specific number of characters in the root font.

rex CSS unit

The rex unit is the root-relative version of ex, equal to the x-height of the root element's font. This unit is particularly useful for vertical alignment and sizing elements relative to the height of lowercase letters in your document's primary typography.

ric CSS unit

The ric unit is the root-relative counterpart to the ic unit. It is equal to the "ideographic" advance measure (typically the width or height of a CJK ideograph) of the root element's font. This is a vital tool for developers building internationalized layouts, particularly those using Chinese, Japanese, or Korean scripts.

Baseline Widely available features

The following web features became Baseline Widely available in January 2026.

Two value CSS display property

The multi-keyword syntax for the display property is now Baseline Widely available. This update lets you explicitly define both the "outer" and "inner" display types of a box. For example, instead of the precomposed inline-flex, you can use display: inline flex. This clarifies whether an element participates in block or inline flow (the outer type) and how its children are laid out (the inner type, like flex or grid). This change makes the CSS layout engine more logical and consistent for developers.

The animation-composition CSS property

The animation-composition property defines how multiple animations should interact when they affect the same property simultaneously. You can choose between replace, add, or accumulate, giving you precise control over how complex, layered animations are calculated.

Array by copy

JavaScript now includes methods that let you transform arrays without mutating the original data. Methods like toReversed(), toSorted(), and toSpliced() return a new, modified copy of the array, promoting a more functional and safer programming style.

Help us improve

As usual, let us know if we missed anything Baseline-related, and we'll make sure it gets captured in a future edition! If you have any questions or want to provide feedback on Baseline, you can file an issue in our issue tracker.