diff --git a/lib/block-supports/layout.php b/lib/block-supports/layout.php
index e607d9c70e55e..9d27ece06e30c 100644
--- a/lib/block-supports/layout.php
+++ b/lib/block-supports/layout.php
@@ -174,6 +174,11 @@ function gutenberg_render_layout_support_flag( $block_content, $block ) {
 	$container_class    = wp_unique_id( 'wp-container-' );
 	$layout_classname   = '';
 
+	// Add a classname to blocks with flow layout set.
+	if ( isset( $used_layout['inherit'] ) && $used_layout['inherit'] || isset( $used_layout['contentSize'] ) && $used_layout['contentSize'] ) {
+		$class_names[] = 'has-content-size';
+	}
+
 	// The following section was added to reintroduce a small set of layout classnames that were
 	// removed in the 5.9 release (https://github.com/WordPress/gutenberg/issues/38719). It is
 	// not intended to provide an extended set of classes to match all block layout attributes
diff --git a/lib/compat/wordpress-6.1/class-wp-theme-json-6-1.php b/lib/compat/wordpress-6.1/class-wp-theme-json-6-1.php
index 293f9640897a3..56ea92c3d2343 100644
--- a/lib/compat/wordpress-6.1/class-wp-theme-json-6-1.php
+++ b/lib/compat/wordpress-6.1/class-wp-theme-json-6-1.php
@@ -697,9 +697,9 @@ public function get_styles_for_block( $block_metadata ) {
 
 			if ( $use_root_vars ) {
 				$block_rules .= '.wp-site-blocks { padding-top: var(--wp--style--root--padding-top); padding-bottom: var(--wp--style--root--padding-bottom); }';
-				$block_rules .= '.wp-site-blocks > * { padding-right: var(--wp--style--root--padding-right); padding-left: var(--wp--style--root--padding-left); }';
-				$block_rules .= '.wp-site-blocks > * > .alignfull { margin-right: calc(var(--wp--style--root--padding-right) * -1); margin-left: calc(var(--wp--style--root--padding-left) * -1); }';
-				$block_rules .= '.alignfull > :where([class*="wp-block-"]:not(.alignfull),p,h1,h2,h3,h4,h5,h6, ul,ol) { padding-right: var(--wp--style--root--padding-right); padding-left: var(--wp--style--root--padding-left); }';
+				$block_rules .= '.has-content-size { padding-right: var(--wp--style--root--padding-right); padding-left: var(--wp--style--root--padding-left); }';
+				$block_rules .= '.has-content-size > .alignfull { margin-right: calc(var(--wp--style--root--padding-right) * -1); margin-left: calc(var(--wp--style--root--padding-left) * -1); }';
+				$block_rules .= '.alignfull > :where([class*="wp-block-"]:not(.alignfull),p,h1,h2,h3,h4,h5,h6,ul,ol) { padding-right: var(--wp--style--root--padding-right); padding-left: var(--wp--style--root--padding-left); }';
 			}
 
 			$block_rules .= '.wp-site-blocks > .alignleft { float: left; margin-right: 2em; }';
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 cf693754495ef..2a0c9ea4de976 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
@@ -531,7 +531,7 @@ export const toStyles = (
 
 	if ( useRootVars ) {
 		ruleset =
-			'body { margin: 0; padding-right: 0; padding-left: 0; padding-top: var(--wp--style--root--padding-top); padding-bottom: var(--wp--style--root--padding-bottom) } .wp-site-blocks > * { padding-right: var(--wp--style--root--padding-right); padding-left: var(--wp--style--root--padding-left); } .wp-site-blocks > * > .alignfull { margin-right: calc(var(--wp--style--root--padding-right) * -1); margin-left: calc(var(--wp--style--root--padding-left) * -1); } .alignfull > :where([class*="wp-block-"]:not(.alignfull),p,h1,h2,h3,h4,h5,h6, ul,ol) { padding-right: var(--wp--style--root--padding-right); padding-left: var(--wp--style--root--padding-left); }';
+			'body { margin: 0; padding-right: 0; padding-left: 0; padding-top: var(--wp--style--root--padding-top); padding-bottom: var(--wp--style--root--padding-bottom) } .has-content-size { padding-right: var(--wp--style--root--padding-right); padding-left: var(--wp--style--root--padding-left); } .has-content-size > .alignfull { margin-right: calc(var(--wp--style--root--padding-right) * -1); margin-left: calc(var(--wp--style--root--padding-left) * -1); } .alignfull > :where([class*="wp-block-"]:not(.alignfull),p,h1,h2,h3,h4,h5,h6, ul,ol) { padding-right: var(--wp--style--root--padding-right); padding-left: var(--wp--style--root--padding-left); }';
 	}
 
 	nodesWithStyles.forEach(