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const nav = document.querySelector('#main');
    let topOfNav = nav.offsetTop;

    function fixNav() {
      if (window.scrollY >= topOfNav) {
        document.body.style.paddingTop = nav.offsetHeight + 'px';
        document.body.classList.add('fixed-nav');
      } else {
        document.body.classList.remove('fixed-nav');
        document.body.style.paddingTop = 0;
      }
    }

    window.addEventListener('scroll', fixNav);