window.onload = function() {
    var headerElement = document.getElementById('customHeader');
    var menuElement = document.getElementsByClassName('customMegaMenu');
    var height = headerElement.offsetHeight; //获取元素的高度，包括边框、内边距和滚动条
    for(var i = 0; i < menuElement.length; i++) {
      menuElement[i].style.top = (height - 1) + 'px'
    }
  }