HTML二级菜单和轮播图

HTML二级菜单和轮播图可以通过CSS和JavaScript实现。以下是一个简单的例子：

HTML代码：

<div class="menu">
  <ul>
    <li><a href="#">菜单1</a>
      <ul>
        <li><a href="#">子菜单1</a></li>
        <li><a href="#">子菜单2</a></li>
        <li><a href="#">子菜单3</a></li>
      </ul>
    </li>
    <li><a href="#">菜单2</a></li>
    <li><a href="#">菜单3</a>
      <ul>
        <li><a href="#">子菜单1</a></li>
        <li><a href="#">子菜单2</a></li>
      </ul>
    </li>
  </ul>
</div>

<div class="slideshow-container">
  <div class="mySlides fade">
    <img src="img1.jpg" style="width:100%">
  </div>

  <div class="mySlides fade">
    <img src="img2.jpg" style="width:100%">
  </div>

  <div class="mySlides fade">
    <img src="img3.jpg" style="width:100%">
  </div>

  <a class="prev" onclick="plusSlides(-1)">&#10094;</a>
  <a class="next" onclick="plusSlides(1)">&#10095;</a>
</div>

CSS代码：

/* 二级菜单样式 */
.menu ul {
  list-style: none;
  margin: 0;
  padding: 0;
  background-color: #f2f2f2;
}

.menu li {
  display: inline-block;
  position: relative;
  padding: 10px 20px;
}

.menu ul ul {
  display: none;
  position: absolute;
  top: 100%;
  left: 0;
  background-color: #fff;
  border: 1px solid #ccc;
  padding: 10px;
}

.menu ul ul li {
  display: block;
  width: 200px;
}

.menu li:hover > ul {
  display:inherit;
}

/* 轮播图样式 */
.slideshow-container {
  max-width: 1000px;
  position: relative;
  margin: auto;
}

.mySlides {
  display: none;
}

.prev, .next {
  cursor: pointer;
  position: absolute;
  top: 50%;
  width: auto;
  margin-top: -22px;
  padding: 16px;
  color: white;
  font-weight: bold;
  font-size: 18px;
  transition: 0.6s ease;
  border-radius: 0 3px 3px 0;
  user-select: none;
}

.next {
  right: 0;
  border-radius: 3px 0 0 3px;
}

.prev:hover, .next:hover {
  background-color: rgba(0,0,0,0.8);
}

.fade {
  -webkit-animation-name: fade;
  -webkit-animation-duration: 1.5s;
  animation-name: fade;
  animation-duration: 1.5s;
}

@-webkit-keyframes fade {
  from {opacity: .4}
  to {opacity: 1}
}

@keyframes fade {
  from {opacity: .4}
  to {opacity: 1}
}

JavaScript代码：

// 轮播图JavaScript代码
var slideIndex = 1;
showSlides(slideIndex);

function plusSlides(n) {
  showSlides(slideIndex += n);
}

function currentSlide(n) {
  showSlides(slideIndex = n);
}

function showSlides(n) {
  var i;
  var slides = document.getElementsByClassName("mySlides");
  var dots = document.getElementsByClassName("dot");
  if (n > slides.length) {slideIndex = 1}
  if (n < 1) {slideIndex = slides.length}
  for (i = 0; i < slides.length; i++) {
      slides[i].style.display = "none";
  }
  for (i = 0; i < dots.length; i++) {
      dots[i].className = dots[i].className.replace(" active", "");
  }
  slides[slideIndex-1].style.display = "block";
  dots[slideIndex-1].className += " active";
}

// 二级菜单JavaScript代码
var dropdown = document.getElementsByClassName("dropdown-btn");
var i;

for (i = 0; i < dropdown.length; i++) {
  dropdown[i].addEventListener("click", function() {
    this.classList.toggle("active");
    var dropdownContent = this.nextElementSibling;
    if (dropdownContent.style.display === "block") {
      dropdownContent.style.display = "none";
    } else {
      dropdownContent.style.display = "block";
    }
  });
}