diff --git a/wp-includes/block-editor.php b/wp-includes/block-editor.php
index af873178eb..18152756d5 100644
--- a/wp-includes/block-editor.php
+++ b/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' );
 	}
 
+	$editor_settings['canEditCSS'] = current_user_can( 'edit_css' );
+
 	return $editor_settings;
 }
 
diff --git a/wp-includes/block-supports/custom-css.php b/wp-includes/block-supports/custom-css.php
new file mode 100644
index 0000000000..9d5b13426f
--- /dev/null
+++ b/wp-includes/block-supports/custom-css.php
@@ -0,0 +1,133 @@
+<?php
+/**
+ * Custom CSS block support.
+ *
+ * @package WordPress
+ */
+
+/**
+ * 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 wp_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::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 wp_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 `wp_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 wp_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( 'has-custom-css' );
+		$tags->add_class( $matches[0] );
+	}
+
+	return $tags->get_updated_html();
+}
+
+add_filter( 'render_block', 'wp_render_custom_css_class_name', 10, 2 );
+add_filter( 'render_block_data', 'wp_render_custom_css_support_styles', 10, 1 );
+add_action( 'wp_enqueue_scripts', 'wp_enqueue_block_custom_css', 1 );
+
+/**
+ * Registers the style block attribute for block types that support it.
+ *
+ * @param WP_Block_Type $block_type Block Type.
+ */
+function wp_register_custom_css_support( $block_type ) {
+	// Setup attributes and styles within that if needed.
+	if ( ! $block_type->attributes ) {
+		$block_type->attributes = array();
+	}
+
+	// Check for existing style attribute definition e.g. from block.json.
+	if ( array_key_exists( 'style', $block_type->attributes ) ) {
+		return;
+	}
+
+	$has_custom_css_support = block_has_support( $block_type, array( 'customCSS' ), true );
+
+	if ( $has_custom_css_support ) {
+		$block_type->attributes['style'] = array(
+			'type' => 'object',
+		);
+	}
+}
+
+// Register the block support.
+WP_Block_Supports::get_instance()->register(
+	'custom-css',
+	array(
+		'register_attribute' => 'wp_register_custom_css_support',
+	)
+);
diff --git a/wp-includes/class-wp-theme-json.php b/wp-includes/class-wp-theme-json.php
index c7929dad9e..b989bab4a6 100644
--- a/wp-includes/class-wp-theme-json.php
+++ b/wp-includes/class-wp-theme-json.php
@@ -1520,12 +1520,13 @@ class WP_Theme_JSON {
 	 *
 	 * @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 static function process_blocks_custom_css( $css, $selector ) {
 		$processed_css = '';
 
 		if ( empty( $css ) ) {
diff --git a/wp-includes/version.php b/wp-includes/version.php
index c4d361c62d..fb3e782b6f 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '7.0-alpha-61677';
+$wp_version = '7.0-alpha-61678';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.
diff --git a/wp-settings.php b/wp-settings.php
index a85536345a..b437ae153b 100644
--- a/wp-settings.php
+++ b/wp-settings.php
@@ -415,6 +415,7 @@ require ABSPATH . WPINC . '/block-supports/block-style-variations.php';
 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';