fix mobile layout

src/components/Sidebar.astro

@@ -27,7 +27,8 @@ import Header from "./Header.astro";
     /* mobile */
     @media screen and (max-width: 600px) {
         .sidebar {
-            position: initial;
+            /* needed due to background being fixed */
+            position: relative;
             height: auto;
         }
     }