include script for sidenav height

src/utils/head-scripts/offline-ui/sidenav.js

@@ -0,0 +1,22 @@
+/**
+ * For offline HTML builds, sidenav should adjust to scroll position
+ * so that it is sticky, but takes up full height when scrolled down
+ * and leaves room for Header Navigation at initial scrollY 0
+ */
+
+function updateSidenavHeight() {
+  const updateScrollY = () => {
+    // pulled from SIDE_NAV_CONTAINER_ID
+    // 'docs-side-nav-container'
+    const sidenavElm = document.querySelector('#docs-side-nav-container');
+    sidenavElm.style = `--scroll-y: ${window.scrollY}px`;
+    window.addEventListener('scroll', (e) => {
+      sidenavElm.style = `--scroll-y: ${e.currentTarget.scrollY}px`;
+    });
+  };
+
+  // TODO: account for multiple browsers here. Which are we supporting? verify with PD
+  document.addEventListener('DOMContentLoaded', updateScrollY, false);
+}
+
+export default updateSidenavHeight;