Smooth Anchor Scrolling with Header Offset

(function () {
  'use strict';

  var OFFSET = 80; // pixels — adjust to match your fixed header height

  document.addEventListener('DOMContentLoaded', function () {
    document.querySelectorAll('a[href^="#"]').forEach(function (anchor) {
      anchor.addEventListener('click', function (e) {
        var hash = anchor.getAttribute('href');
        if (hash === '#') return;
        var target = document.querySelector(hash);
        if (!target) return;
        e.preventDefault();
        var top = target.getBoundingClientRect().top + window.scrollY - OFFSET;
        window.scrollTo({ top: top, behavior: 'smooth' });
        history.pushState(null, '', hash);
        target.setAttribute('tabindex', '-1');
        target.focus({ preventScroll: true });
      });
    });
  });
})();