Editor style is no longer working

[iamtakashi]

Description

With Gutenberg trunk, the stylesheet added via add_editor_style() is no longer working.

Step-by-step reproduction instructions

For example, TT5 has a editor-style.css, and to make it easier to see the difference, let's make h1 have a red background :)

h1 {
	background-color: red;
}

Save the CSS and open the editor.

No h1 has the red background in the editor.

If you disable the plugin, we can see a h1 with a red background.

Screenshots, screen recording, code snippet

No response

Environment info

WP 6.9
Gutenberg trunk

Please confirm that you have searched existing issues in the repo.

• Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

• Yes

Please confirm which theme type you used for testing.

• Block
• Classic
• Hybrid (e.g. classic with theme.json)
• Not sure

[annezazu]

I ran into this last night and you beat me to an issue! @ramonjd can your crew check this out?

[ramonjd]

I failed to reproduce on the following:

• Gutenberg Trunk + WordPress Core trunk
• Gutenberg Trunk + WordPress 6.9
• WordPress Core trunk (plugin disabled)
• WordPress 6.9 (plugin disabled)

I tested updating the stylesheet that was imported via add_editor_style in TT5, TT4 (created a custom one) and Gutenberg's empty theme.

/*
// path/to/sweet.css contains:
h1 {
	background-color: yellow;
}

p {
	font-size: 200px;
}
*/

add_action( 'init', 'twentytwentyfour_pattern_categories' );
if ( ! function_exists( 'a_sweet_editor_style' ) ) {
	function a_sweet_editor_style() {
		add_editor_style( 'path/to/sweet.css' );
	}
}

add_action( 'after_setup_theme', 'a_sweet_editor_style' );

The styles are being loaded by wp.editPost.initializeEditor in the source HTML.

Playground (same results for 6.9 and 6.9 + Gutenberg)

Kapture.2025-12-18.at.12.26.06.mp4

Do folks have any more details?

Let's check:

• which filter is running when using add_editor_style
• are there any Core styles that overwrite what you're trying to do? (for example, body > background-color might not work for example as it's being overwritten by theme.json/global styles/core editor css)
• are any other styles or themes working?

[iamtakashi]

@ramonjd Thanks for your help. I noticed you tested it in the post/page editor. The problem I'm having is with the site editor. Could you check the site editor again?

[ramonjd]

Thanks for the specifics! I reran my tests above but with the site editor, and it looks like Gutenberg trunk is the culprit and not add_editor_style itself.

And it looks like my PR did this!

I think have a fix.

[ramonjd]

And it looks like #73952 did this!

Actually, a bit of mine and a bit of #72681

[annezazu]

Thanks so much for diving into this so promptly ✨

[ramonjd]

Thanks so much for diving into this so promptly ✨

No worries, lucky it turned out to be something I'm recently familiar with 🤞🏻