Assembler color styles are not applied properly within Safari

[richtabor]

Steps to reproduce

1. Open Safari
2. Starting at URL: https://wordpress.com/setup/with-theme-assembler/pattern-assembler
3. Add two patterns to the page.
4. Select "Select styles"
5. Select a premium style with a background color.

What I expected

To see the background color of the style applied to my patterns. It works as expected in Chrome.

What happened instead

The patterns maintain a background color of white, making it seem like the style is much less expressive and boring.

Browser / OS version

Safari, latest.

Screenshot / Video

[taipeicoder]

Sharing my findings below:

This issue is caused by a recent change in Gutenberg WordPress/gutenberg#59377 where the iframe body is explicitly set to have a white background. This was later fixed in WordPress/gutenberg#60106 where the CSS rule's specificity was reduced. Fixing this on Calypso side would require a version upgrade of the @wordpress/block-editor version from 12.22.0 to 12.23.0.

I've requested assistance from the Calypso team in #89343 (comment) for the package upgrade.