diff -r 48c4eec2b7e6 -r 8c2e4d02f4ef wp/wp-includes/class-wp-theme-json-resolver.php
--- a/wp/wp-includes/class-wp-theme-json-resolver.php	Fri Sep 05 18:40:08 2025 +0200
+++ b/wp/wp-includes/class-wp-theme-json-resolver.php	Fri Sep 05 18:52:52 2025 +0200
@@ -848,6 +848,7 @@
 	 * as the value of `_link` object in REST API responses.
 	 *
 	 * @since 6.6.0
+	 * @since 6.7.0 Resolve relative paths in block styles.
 	 *
 	 * @param WP_Theme_JSON $theme_json A theme json instance.
 	 * @return array An array of resolved paths.
@@ -860,15 +861,14 @@
 		}
 
 		$theme_json_data = $theme_json->get_raw_data();
-
-		// Top level styles.
-		$background_image_url = isset( $theme_json_data['styles']['background']['backgroundImage']['url'] ) ? $theme_json_data['styles']['background']['backgroundImage']['url'] : null;
-
 		/*
 		 * The same file convention when registering web fonts.
 		 * See: WP_Font_Face_Resolver::to_theme_file_uri.
 		 */
 		$placeholder = 'file:./';
+
+		// Top level styles.
+		$background_image_url = $theme_json_data['styles']['background']['backgroundImage']['url'] ?? null;
 		if (
 			isset( $background_image_url ) &&
 			is_string( $background_image_url ) &&
@@ -888,6 +888,33 @@
 			$resolved_theme_uris[] = $resolved_theme_uri;
 		}
 
+		// Block styles.
+		if ( ! empty( $theme_json_data['styles']['blocks'] ) ) {
+			foreach ( $theme_json_data['styles']['blocks'] as $block_name => $block_styles ) {
+				if ( ! isset( $block_styles['background']['backgroundImage']['url'] ) ) {
+					continue;
+				}
+				$background_image_url = $block_styles['background']['backgroundImage']['url'];
+				if (
+					is_string( $background_image_url ) &&
+					// Skip if the src doesn't start with the placeholder, as there's nothing to replace.
+					str_starts_with( $background_image_url, $placeholder )
+				) {
+					$file_type          = wp_check_filetype( $background_image_url );
+					$src_url            = str_replace( $placeholder, '', $background_image_url );
+					$resolved_theme_uri = array(
+						'name'   => $background_image_url,
+						'href'   => sanitize_url( get_theme_file_uri( $src_url ) ),
+						'target' => "styles.blocks.{$block_name}.background.backgroundImage.url",
+					);
+					if ( isset( $file_type['type'] ) ) {
+						$resolved_theme_uri['type'] = $file_type['type'];
+					}
+					$resolved_theme_uris[] = $resolved_theme_uri;
+				}
+			}
+		}
+
 		return $resolved_theme_uris;
 	}
 
@@ -906,18 +933,14 @@
 			return $theme_json;
 		}
 
-		$resolved_theme_json_data = array(
-			'version' => WP_Theme_JSON::LATEST_SCHEMA,
-		);
+		$resolved_theme_json_data = $theme_json->get_raw_data();
 
 		foreach ( $resolved_urls as $resolved_url ) {
 			$path = explode( '.', $resolved_url['target'] );
 			_wp_array_set( $resolved_theme_json_data, $path, $resolved_url['href'] );
 		}
 
-		$theme_json->merge( new WP_Theme_JSON( $resolved_theme_json_data ) );
-
-		return $theme_json;
+		return new WP_Theme_JSON( $resolved_theme_json_data );
 	}
 
 	/**