如何在bootstrap粘性下拉标头上保持底部边框？

.sticky-header {
  position: sticky;
  top: 0;
  border-bottom: 1px solid #000;
}

.sticky-container {
  position: relative;
}

// 纯 JavaScript 示例
window.addEventListener('scroll', function() {
  var header = document.getElementById('header');
  var headerOffset = header.offsetTop;
  
  if (window.pageYOffset > headerOffset) {
    header.classList.add('sticky-header');
  } else {
    header.classList.remove('sticky-header');
  }
});

// jQuery 示例
$(window).scroll(function() {
  var header = $('#header');
  var headerOffset = header.offset().top;
  
  if ($(window).scrollTop() > headerOffset) {
    header.addClass('sticky-header');
  } else {
    header.removeClass('sticky-header');
  }
});