Move fixed CSS syntax files to archive

Author: jacobcassidy

.dev-assets/syntax-issues/at-layer.css renamed to .dev-assets/syntax-issues/archive/at-layer.css

@@ -2,6 +2,10 @@
  * AT PAGE
  */
 
+@page {
+  content: "Page " counter(pageNumber);
+}
+
 @page {
   /* margin box at top right showing page number */
   @top-right {