diff --git a/wp-includes/class-wp-theme-json.php b/wp-includes/class-wp-theme-json.php
index cf56000f87..1af02531cc 100644
--- a/wp-includes/class-wp-theme-json.php
+++ b/wp-includes/class-wp-theme-json.php
@@ -3495,7 +3495,7 @@ class WP_Theme_JSON {
 		$prefix_len = strlen( $prefix );
 		$token_in   = '|';
 		$token_out  = '--';
-		if ( 0 === strpos( $value, $prefix ) ) {
+		if ( str_starts_with( $value, $prefix ) ) {
 			$unwrapped_name = str_replace(
 				$token_in,
 				$token_out,
@@ -3519,7 +3519,7 @@ class WP_Theme_JSON {
 		$prefix = 'var:';
 
 		foreach ( $tree as $key => $data ) {
-			if ( is_string( $data ) && 0 === strpos( $data, $prefix ) ) {
+			if ( is_string( $data ) && str_starts_with( $data, $prefix ) ) {
 				$tree[ $key ] = self::convert_custom_properties( $data );
 			} elseif ( is_array( $data ) ) {
 				$tree[ $key ] = self::resolve_custom_css_format( $data );
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 3fc98c403d..435d15ed3b 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.3-alpha-55986';
+$wp_version = '6.3-alpha-55987';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.