Gutenberg Backport - Block level custom CSS

src/wp-includes/block-editor.php

@@ -658,6 +658,8 @@ function get_block_editor_settings( array $custom_settings, $block_editor_contex
 		$editor_settings = apply_filters_deprecated( 'block_editor_settings', array( $editor_settings, $post ), '5.8.0', 'block_editor_settings_all' );
 	}
 
+	$settings['canEditCSS'] = current_user_can( 'edit_css' );
+
 	return $editor_settings;
 }
 

src/wp-includes/block-supports/custom-css.php

@@ -0,0 +1,99 @@
+<?php
+/**
+ * Custom CSS block support.
+ *
+ * @package gutenberg
+ */
+
+/**
+ * Render the custom CSS stylesheet and add class name to block as required.
+ *
+ * @since 7.0.0
+ *
+ * @param array $parsed_block The parsed block.
+ * @return array The same parsed block with custom CSS class name added if appropriate.
+ */
+function gutenberg_render_custom_css_support_styles( $parsed_block ) {
+	$block_type = WP_Block_Type_Registry::get_instance()->get_registered( $parsed_block['blockName'] );
+
+	if ( ! block_has_support( $block_type, 'customCSS', true ) ) {
+		return $parsed_block;
+	}
+
+	$custom_css = trim( $parsed_block['attrs']['style']['css'] ?? '' );
+
+	if ( empty( $custom_css ) ) {
+		return $parsed_block;
+	}
+
+	// Validate CSS doesn't contain HTML markup (same validation as global styles REST API).
+	if ( preg_match( '#</?\w+#', $custom_css ) ) {
+		return $parsed_block;
+	}
+
+	// Generate a unique class name for this block instance.
+	$class_name         = wp_unique_id_from_values( $parsed_block, 'wp-custom-css-' );
+	$updated_class_name = isset( $parsed_block['attrs']['className'] )
+		? $parsed_block['attrs']['className'] . " $class_name"
+		: $class_name;
+
+	_wp_array_set( $parsed_block, array( 'attrs', 'className' ), $updated_class_name );
+
+	// Process the custom CSS using the same method as global styles.
+	$selector      = '.' . $class_name;
+	$processed_css = WP_Theme_JSON_Gutenberg::process_blocks_custom_css( $custom_css, $selector );
+
+	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.
+		 */
+		wp_register_style( 'wp-block-custom-css', false, array( 'global-styles' ) );
+		wp_add_inline_style( 'wp-block-custom-css', $processed_css );
+	}
+
+	return $parsed_block;
+}
+
+/**
+ * Enqueues the block custom CSS styles.
+ *
+ * @since 7.0.0
+ */
+function gutenberg_enqueue_block_custom_css() {
+	wp_enqueue_style( 'wp-block-custom-css' );
+}
+
+/**
+ * Applies the custom CSS class name to the block's rendered HTML.
+ *
+ * The class name is generated in `gutenberg_render_custom_css_support_styles`
+ * and stored in block attributes. This filter adds it to the actual markup.
+ *
+ * @since 7.0.0
+ *
+ * @param string $block_content Rendered block content.
+ * @param array  $block         Block object.
+ * @return string               Filtered block content.
+ */
+function gutenberg_render_custom_css_class_name( $block_content, $block ) {
+	$class_string = $block['attrs']['className'] ?? '';
+	preg_match( '/\bwp-custom-css-\S+\b/', $class_string, $matches );
+
+	if ( empty( $matches ) ) {
+		return $block_content;
+	}
+
+	$tags = new WP_HTML_Tag_Processor( $block_content );
+
+	if ( $tags->next_tag() ) {
+		$tags->add_class( $matches[0] );
+	}
+
+	return $tags->get_updated_html();
+}
+
+add_filter( 'render_block', 'gutenberg_render_custom_css_class_name', 10, 2 );
+add_filter( 'render_block_data', 'gutenberg_render_custom_css_support_styles', 10, 1 );
+add_action( 'wp_enqueue_scripts', 'gutenberg_enqueue_block_custom_css', 1 );

src/wp-includes/class-wp-theme-json.php

@@ -1420,12 +1420,13 @@ public function get_stylesheet( $types = array( 'variables', 'styles', 'presets'
 	 *
 	 * @since 6.2.0
 	 * @since 6.6.0 Enforced 0-1-0 specificity for block custom CSS selectors.
+	 * @since 7.0.0 Made public for use in custom-css block support.
 	 *
 	 * @param string $css      The CSS to process.
 	 * @param string $selector The selector to nest.
 	 * @return string The processed CSS.
 	 */
-	protected function process_blocks_custom_css( $css, $selector ) {
+	public function process_blocks_custom_css( $css, $selector ) {
 		$processed_css = '';
 
 		if ( empty( $css ) ) {

src/wp-settings.php

@@ -412,6 +412,7 @@
 require ABSPATH . WPINC . '/block-supports/aria-label.php';
 require ABSPATH . WPINC . '/block-supports/anchor.php';
 require ABSPATH . WPINC . '/block-supports/block-visibility.php';
+require ABSPATH . WPINC . '/block-supports/custom-css.php';
 require ABSPATH . WPINC . '/style-engine.php';
 require ABSPATH . WPINC . '/style-engine/class-wp-style-engine.php';
 require ABSPATH . WPINC . '/style-engine/class-wp-style-engine-css-declarations.php';