text: var viewportHeader = document.querySelector(".viewport-header");
  
  document.body.addEventListener("scroll", function(event) {
    var opacity = (document.body.offsetHeight - document.body.scrollTop) / document.body.offsetHeight;
    var scale = (document.body.offsetHeight - document.body.scrollTop) / document.body.offsetHeight;
    document.documentElement.style.setProperty('--headerOpacity', opacity);
    document.documentElement.style.setProperty('--headerScale', scale);
  });