im lazy writing commit messagesm please take a look by yourself thx

public/js/nav.js

@@ -10,4 +10,27 @@ function applyHeaderShadow() {
     }
   });
 }
-document.addEventListener("DOMContentLoaded", applyHeaderShadow);
+document.addEventListener("DOMContentLoaded", applyHeaderShadow);
+
+function applyHeaderAutoHide() {
+  const header = document.querySelector(".web-header-autohide");
+  if (!header) return;
+
+  let lastScrollY = window.scrollY;
+
+  window.addEventListener("scroll", () => {
+    const currentScrollY = window.scrollY;
+
+    if (currentScrollY > lastScrollY && currentScrollY > 0) {
+      // Scrolling down -> hide header
+      header.classList.add("web-header-hidden");
+    } else {
+      // Scrolling up -> show header
+      header.classList.remove("web-header-hidden");
+    }
+
+    lastScrollY = currentScrollY;
+  });
+}
+
+document.addEventListener("DOMContentLoaded", applyHeaderAutoHide);