如何在加载表单时保持在表单顶部？

.form-container {
  position: fixed;
  top: 0;
  width: 100%;
}

window.addEventListener('scroll', function() {
  var formContainer = document.querySelector('.form-container');
  var scrollTop = window.pageYOffset || document.documentElement.scrollTop;
  
  if (scrollTop > formContainer.offsetTop) {
    formContainer.style.position = 'fixed';
    formContainer.style.top = '0';
  } else {
    formContainer.style.position = 'static';
  }
});

$('.form-container').sticky();