customer-riverside/web/modules/custom/riverside_pt/js/scroll.js

import zenscroll from "https://esm.sh/zenscroll@4.0.2";

var FIXED_BUFFER  = 91; // breathing room below fixed header when menu is closed
var MOBILE_BUFFER =  0; // no offset needed when header is in-flow (scrolls away)

// Returns the effective scroll offset to clear the header.
// When the hamburger is open, offsetHeight already includes the expanded nav,
// so no extra buffer is needed. When closed, add FIXED_BUFFER for breathing room.
function headerOffset() {
  var header = document.querySelector(".rpt-header");
  if (!header) return MOBILE_BUFFER;
  var pos = window.getComputedStyle(header).position;
  if (pos !== "fixed" && pos !== "sticky") return MOBILE_BUFFER;
  var nav = document.getElementById("rpt-main-nav");
  var menuOpen = nav && nav.classList.contains("is-open");
  return header.offsetHeight + (menuOpen ? 0 : FIXED_BUFFER);
}

// On load: if the URL has a hash (e.g. /home#pt-services from another page),
// re-scroll with the correct header offset instead of the browser's native jump.
document.addEventListener("DOMContentLoaded", function () {
  if (!window.location.hash) return;
  var target = document.querySelector(window.location.hash);
  if (!target) return;
  // Defer until layout is stable, then position correctly.
  requestAnimationFrame(function () {
    zenscroll.to(target, 0, headerOffset());
  });
});

document.addEventListener("click", function (e) {
  var link = e.target.closest("[data-scroll-to]");
  if (!link) return;
  var target = document.querySelector(link.dataset.scrollTo);
  if (!target) return;
  e.preventDefault();
  zenscroll.to(target, 400, headerOffset());
});