Tweak overlay header positioning?

Author: zemccartney

src/components/subpage-nav.astro

@@ -107,6 +107,10 @@ import Logo from "./logo.astro";
                 .mobile-overlay {
                     display: block;
                 }
+
+                .mobile-overlay-header {
+                    position: sticky;
+                }
             }
         }