diff --git a/lib/compat/wordpress-6.2/class-wp-theme-json-6-2.php b/lib/compat/wordpress-6.2/class-wp-theme-json-6-2.php
index c5c139dde487d3..bc0bff5841d959 100644
--- a/lib/compat/wordpress-6.2/class-wp-theme-json-6-2.php
+++ b/lib/compat/wordpress-6.2/class-wp-theme-json-6-2.php
@@ -280,6 +280,27 @@ protected static function remove_insecure_styles( $input ) {
 		return $output;
 	}
 
+	/**
+	 * Processes the CSS, to apply nesting.
+	 *
+	 * @param string $css      The CSS to process.
+	 * @param string $selector The selector to nest.
+	 *
+	 * @return string The processed CSS.
+	 */
+	private function process_nested_css( $css, $selector ) {
+		$processed_css = '';
+
+		// Split CSS nested rules.
+		$parts = explode( '&', $css );
+		foreach ( $parts as $part ) {
+			$processed_css .= ( ! str_contains( $part, '{' ) )
+				? $selector . '{' . $part . '}' // If the part doesn't contain braces, it applies to the root level.
+				: $selector . $part; // Prepend the selector, which effectively replaces the "&" character.
+		}
+		return $processed_css;
+	}
+
 	/**
 	 * Returns the stylesheet that results of processing
 	 * the theme.json structure this object represents.
@@ -383,15 +404,16 @@ public function get_stylesheet( $types = array( 'variables', 'styles', 'presets'
 
 		// Load the custom CSS last so it has the highest specificity.
 		if ( in_array( 'custom-css', $types, true ) ) {
-			// Add the global styles root CSS:
+			// Add the global styles root CSS.
 			$stylesheet .= _wp_array_get( $this->theme_json, array( 'styles', 'css' ) );
 
 			// Add the global styles block CSS.
-			foreach ( $this->theme_json['styles']['blocks'] as $name => $node )
+			foreach ( $this->theme_json['styles']['blocks'] as $name => $node ) {
 				if ( _wp_array_get( $this->theme_json, array( 'styles', 'blocks', $name, 'css' ) ) ) {
-				$selector = static::$blocks_metadata[ $name ]['selector'];
-				$custom_block_css = _wp_array_get( $this->theme_json, array( 'styles', 'blocks', $name, 'css' ) );
-				$stylesheet .= $selector . '{' . $custom_block_css . '}';
+					$selector         = static::$blocks_metadata[ $name ]['selector'];
+					$custom_block_css = _wp_array_get( $this->theme_json, array( 'styles', 'blocks', $name, 'css' ) );
+					$stylesheet      .= $this->process_nested_css( $custom_block_css, $selector );
+				}
 			}
 		}
 
diff --git a/packages/edit-site/src/components/global-styles/use-global-styles-output.js b/packages/edit-site/src/components/global-styles/use-global-styles-output.js
index 93ee152d5839c5..b10e6e090ab32e 100644
--- a/packages/edit-site/src/components/global-styles/use-global-styles-output.js
+++ b/packages/edit-site/src/components/global-styles/use-global-styles-output.js
@@ -939,6 +939,19 @@ export function useGlobalStylesOutput() {
 			},
 		];
 
+		const processCSSNesting = ( css, blockSelector ) => {
+			let processedCSS = '';
+
+			// Split CSS nested rules.
+			const parts = css.split( '&' );
+			parts.forEach( ( part ) => {
+				processedCSS += ! part.includes( '{' )
+					? blockSelector + '{' + part + '}' // If the part doesn't contain braces, it applies to the root level.
+					: blockSelector + part; // Prepend the selector, which effectively replaces the "&" character.
+			} );
+			return processedCSS;
+		};
+
 		// Loop through the blocks to check if there are custom CSS values.
 		// If there are, get the block selector and push the selector together with
 		// the CSS value to the 'stylesheets' array.
@@ -946,11 +959,10 @@ export function useGlobalStylesOutput() {
 			if ( mergedConfig.styles.blocks[ name[ 0 ] ]?.css ) {
 				const selector = blockSelectors[ name[ 0 ] ].selector;
 				stylesheets.push( {
-					css:
-						selector +
-						'{' +
-						mergedConfig.styles.blocks[ name[ 0 ] ]?.css +
-						'}',
+					css: processCSSNesting(
+						mergedConfig.styles.blocks[ name[ 0 ] ]?.css,
+						selector
+					),
 					isGlobalStyles: true,
 				} );
 			}