diff --git a/samples/csharp_dotnetcore/06.using-cards/wwwroot/default.htm b/samples/csharp_dotnetcore/06.using-cards/wwwroot/default.htm
index f1813cd1a2..419ab6e820 100644
--- a/samples/csharp_dotnetcore/06.using-cards/wwwroot/default.htm
+++ b/samples/csharp_dotnetcore/06.using-cards/wwwroot/default.htm
@@ -264,7 +264,7 @@
             }
 
             .header-text {
-                font-size: 40x;
+                font-size: 40px;
             }
 
             .column {