Added subnavbar.

Scripts/SubNavbar.js

@@ -0,0 +1,93 @@
+function StartSubNavbar() {
+    const SubNavbar =
+        document.querySelector(
+            ".SubNavbar"
+        );
+
+    if (SubNavbar === null) {
+        return;
+    }
+
+    const Links = [
+        ...SubNavbar.querySelectorAll(
+            ".SubNavbarLink"
+        )
+    ];
+
+    const AnchorLinks =
+        Links.filter(
+            Link =>
+                Link.getAttribute(
+                    "href"
+                )?.startsWith("#")
+        );
+
+
+    function SetCurrentLink(
+        CurrentLink
+    ) {
+        for (
+            const Link
+            of AnchorLinks
+        ) {
+            Link.removeAttribute(
+                "aria-current"
+            );
+        }
+
+        if (CurrentLink !== null) {
+            CurrentLink.setAttribute(
+                "aria-current",
+                "location"
+            );
+        }
+    }
+
+
+    function UpdateFromHash() {
+        if (location.hash === "") {
+            return;
+        }
+
+        const CurrentLink =
+            AnchorLinks.find(
+                Link =>
+                    Link.getAttribute(
+                        "href"
+                    ) === location.hash
+            ) ?? null;
+
+        SetCurrentLink(
+            CurrentLink
+        );
+    }
+
+
+    for (
+        const Link
+        of AnchorLinks
+    ) {
+        Link.addEventListener(
+            "click",
+            () => {
+                SetCurrentLink(
+                    Link
+                );
+            }
+        );
+    }
+
+
+    window.addEventListener(
+        "hashchange",
+        UpdateFromHash
+    );
+
+    UpdateFromHash();
+}
+
+
+document.addEventListener(
+    "DOMContentLoaded",
+    StartSubNavbar
+);