Published: January 22, 2025

As Interop 2024 draws to a close, this post looks back at the most successful
year ever for the project. We ended with all experimental browsers reporting a
score of 99, with the stable versions not far behind. This success means that a
number of features are now Baseline Newly available.

More features to Baseline

For a feature to be Baseline Newly available, it needs to be interoperable. It’s
therefore no surprise that Interop 2024 helped a number of features over that
line and into Baseline 2024.

Registered custom properties

The @property rule and CSS.registerProperty() static method became Baseline
Newly available in July 2024.

The font-size-adjust property

The font-size-adjust CSS property preserves apparent text size, regardless of
the font used, by scaling fonts to the same size with respect to a specific
metric, such as x-height. This can help make fallback fonts look the same size.
It became Baseline Newly available in July 2024.

The requestVideoFrameCallback() method for

The requestVideoFrameCallback() method for schedules a function that
runs with the next video frame. It’s similar to requestAnimationFrame(), but
for video, and became Newly available in October 2024.

Scrollbar styling with scrollbar-width and scrollbar-gutter

The scrollbar-width CSS property sets the width of the scrollbar, and
scrollbar-gutter reserves space for the scrollbar, preventing unwanted layout
changes as the scrollbar appears and disappears. They became Baseline Newly
available in December 2024.

The transition-behavior property

The transition-behavior: allow-discrete CSS declaration allows transitions for
properties whose animation behavior is discrete. Such properties can’t be
interpolated and swap from their start value to the end value at 50%. This
property became Baseline Newly available in August 2024.

text-wrap: balance

The text-wrap CSS property sets how lines break in text that overflows the
container. It is a shorthand for text-wrap-style and text-wrap-mode. The
balance value lets you create balanced headlines and other short pieces of
text. The text-wrap property became Baseline Newly available in March 2024.

Popover

Popover lets you create overlays declaratively using HTML, or with the
showPopover() method. It almost made it to Baseline Newly available, and in
fact we initially thought it had, however an issue with the Safari
implementation meant that it didn’t quite hit Newly available in 2024. The good
news is that the issue is fixed in the current Safari Beta 18.3, so we’ll soon
be able to properly announce Popover as Baseline Newly available.

Fixes to Baseline features

There were features included in Interop 2024 that were already classed as
Baseline Newly available, the work was to fix some small differences in
implementation. These might be things that very few people run into, however
small things make a big difference if it’s you running into them.

CSS nesting

CSS nesting allows for shorter selectors, easier reading, and more modularity by
nesting rules inside others. It became Baseline Newly available in December
2023, and was included in Interop 2024 to fix some outstanding interop issues.

Declarative Shadow DOM

The shadowrootmode attribute on