Post Content Block: Block Style Variation applies on frontend but not in editor when Show Template is switched off

[huubl]

Description

I've registered a custom block style variation for the core/post-content block using a JSON file located at:

[theme]/styles/blocks/post-content-red-headings.json

{
  "$schema": "https://raw.githubusercontent.com/WordPress/gutenberg/trunk/schemas/json/theme.json",
  "version": 3,
  "title": "Post content in red headings",
  "slug": "red-headings",
  "blockTypes": [ "core/post-content" ],
  "description": "Post content with red headings.",
  "styles": {
    "elements": {
      "heading": {
        "color": {
          "text": "#ff0000"
        }
      }
    }
  }
}

When this style variation is applied to the core/post-content block within the page.html template, it renders correctly on the frontend. However, in the Site Editor, the styles are not applied unless the "Show template" option is enabled.

Expected Behavior:

The styles defined in the block style variation JSON should be applied in the Site Editor regardless of the "Show template" setting.

Actual Behavior:

The styles are only applied in the Site Editor when "Show template" is enabled.

Step-by-step reproduction instructions

1. Create the above JSON file in the specified directory.
2. Add <!-- wp:post-content {"className":"is-style-red-headings"} /--> to the page.html template.
3. Open a page and add some headings to the content
4. Observe that the custom styles are not applied in the editor.
5. Enable the "Show template" option.
6. Observe that the custom styles are now applied.

Screenshots, screen recording, code snippet

WordPress.Playground.mp4

Environment info

No response

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

[kushagra-goyal-14]

Hello, I was able to replicate this issue on my environment with the following configurations -

• WordPress: 6.9-alpha-60272
• PHP: 8.2.28
• Server: Apache/2.4.62 (Debian)
• Database: mysqli (Server: 11.4.7-MariaDB-ubu2404 / Client: mysqlnd 8.2.28)
• Browser: Chrome 135.0.0.0
• OS: macOS
• Theme: Twenty Twenty-Five 1.2
• MU Plugins:
  • Gutenberg Test Plugin, Disable Login Autofocus
  • Gutenberg Test Plugin, Disable Remote Patterns
  • Gutenberg Test Plugin, Enable Templates UI
  • Gutenberg Test Plugin, No-cache Headers
  • Gutenberg Test Plugin, Normalize Theme
  • server-timing.php
• Plugins:
  • Gutenberg 21.0.0

Screen.Recording.2025-06-12.at.12.56.25.PM.mov

[talldan]

The styles are only applied in the Site Editor when "Show template" is enabled.

I believe that the core/post-content block is only present in the editor when 'Show Template' is switched on, so that's likely the reason for the issue.

It's an interesting problem! I'm guessing you only want those styles applies to the post content? Otherwise you could consider using a theme style variation.

I'll update the issue title, because I think it's only relevant to that block, but the title makes it sound like it's a problem for any block style variation.