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Block Supports: Prevent Additional CSS duplication inside Query Loop #11859

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Block Supports: Prevent Additional CSS duplication inside Query Loop #11859

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4b81300
Block Supports: Prevent Additional CSS duplication inside Query Loop
Mustafabharmal May 19, 2026
e2b7da3
Reformat block comment indentation in custom-css.php
Mustafabharmal May 19, 2026
7ac1658
Refactor: custom CSS handling to prevent duplicate styles in Query Loop
Mustafabharmal Jun 3, 2026
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19 changes: 14 additions & 5 deletions src/wp-includes/block-supports/custom-css.php
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Original file line number Diff line number Diff line change
Expand Up @@ -57,12 +57,21 @@ function wp_render_custom_css_support_styles( $parsed_block ) {

if ( ! empty( $processed_css ) ) {
/*
* Register and add inline style for block custom CSS.
* The style depends on global-styles to ensure custom CSS loads after
* and can override global styles.
* Track which class names have already had their CSS enqueued to prevent
* duplicate styles when the same block is rendered multiple times inside
* a Query Loop (render_block_data fires once per loop iteration).
Comment on lines +60 to +62

@t-hamano t-hamano Jun 7, 2026

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Suggested change
* Track which class names have already had their CSS enqueued to prevent
* duplicate styles when the same block is rendered multiple times inside
* a Query Loop (render_block_data fires once per loop iteration).
* Skip CSS that has already been added. Blocks with identical attributes
* share the same class name and processed CSS via wp_unique_id_from_values(),
* so the same style would otherwise be enqueued more than once (e.g. inside
* a Query Loop or when blocks share identical custom CSS).

Since this issue is not limited to the Query Loop block, I recommend updating this comments to be more accurate.

For example, create content like the following:

<!-- wp:paragraph {"style":{"css":"background: red;"}} -->
<p class="has-custom-css">Hello World</p>
<!-- /wp:paragraph -->
<!-- wp:paragraph {"style":{"css":"background: red;"}} -->
<p class="has-custom-css">Hello World</p>
<!-- /wp:paragraph -->
<!-- wp:paragraph {"style":{"css":"background: red;"}} -->
<p class="has-custom-css">Hello World</p>
<!-- /wp:paragraph -->
<!-- wp:paragraph {"style":{"css":"background: red;"}} -->
<p class="has-custom-css">Hello World</p>
<!-- /wp:paragraph -->

This PR will eliminate the duplicate CSS.

Before:

<style id="wp-block-custom-css-inline-css">
:root :where(.wp-custom-css-38db0572){background: red;}
:root :where(.wp-custom-css-38db0572){background: red;}
:root :where(.wp-custom-css-38db0572){background: red;}
:root :where(.wp-custom-css-38db0572){background: red;}
</style>

After:

```html
<style id="wp-block-custom-css-inline-css">
:root :where(.wp-custom-css-38db0572){background: red;}
</style>

@westonruter westonruter Jun 7, 2026

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Good call, although I suggest {@see wp_unique_id_from_values()} to link the reference.

*/
wp_register_style( 'wp-block-custom-css', false, array( 'global-styles' ) );
wp_add_inline_style( 'wp-block-custom-css', $processed_css );
$handle = 'wp-block-custom-css';
if ( ! wp_style_is( $handle, 'registered' ) ) {
wp_register_style( $handle, false, array( 'global-styles' ) );
}
$after_styles = wp_styles()->get_data( $handle, 'after' );
if ( ! is_array( $after_styles ) ) {
$after_styles = array();
}
if ( ! in_array( $processed_css, $after_styles, true ) ) {
wp_add_inline_style( $handle, $processed_css );
}
}

return $parsed_block;
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