diff --git a/lib/rdoc/generator/template/darkfish/css/rdoc.css b/lib/rdoc/generator/template/darkfish/css/rdoc.css
index 68e79ed93a..35075b2d60 100644
--- a/lib/rdoc/generator/template/darkfish/css/rdoc.css
+++ b/lib/rdoc/generator/template/darkfish/css/rdoc.css
@@ -534,7 +534,7 @@ main .method-source-code {
 }
 
 main .method-source-code pre {
-  background: var(--source-code-background-color);
+  border-color: var(--source-code-toggle-color);
 }
 
 main .method-source-code.active-menu {