Add style rule once (#23025)

lib/global-styles.php

@@ -439,6 +439,16 @@ function gutenberg_experimental_global_styles_resolver( $tree ) {
 			)
 		);
 	}
+
+	if ( gutenberg_experimental_global_styles_has_theme_json_support() ) {
+		// To support all themes, we added in the block-library stylesheet
+		// a style rule such as .has-link-color a { color: var(--wp--style--color--link, #00e); }
+		// so that existing link colors themes used didn't break.
+		// We add this here to make it work for themes that opt-in to theme.json
+		// In the future, we may do this differently.
+		$stylesheet .= 'a { color: var(--wp--style--color--link, #00e); }';
+	}
+
 	return $stylesheet;
 }
 
@@ -455,15 +465,6 @@ function gutenberg_experimental_global_styles_resolver_styles( $block_selector,
 	$css_rule         = '';
 	$css_declarations = '';
 
-	if ( gutenberg_experimental_global_styles_has_theme_json_support() ) {
-		// To support all themes, we added in the block-library stylesheet
-		// a style rule such as .has-link-color a { color: var(--wp--style--color--link, #00e); }
-		// so that existing link colors themes used didn't break.
-		// We add this here to make it work for themes that opt-in to theme.json
-		// In the future, we may do this differently.
-		$css_rule = 'a { color: var(--wp--style--color--link, #00e); }';
-	}
-
 	foreach ( $block_styles as $property => $value ) {
 		// Only convert to CSS:
 		//