实现焦点轮播图的效果，有01.jpg，02.jpg，03.jpg三张图片，要求如下：1.当页面加载完成后，三张图片每2秒自动切换一张图片，2.切换图片时，其对应按钮的样式同步变换——背景颜色变成红色，3.当鼠标悬停在某个按钮上时，显示该按钮对应的图片且轮播停止，给出完整代码

HTML代码：

<div class="carousel">
  <ul class="carousel-list">
    <li class="carousel-item"><img src="01.jpg" alt=""></li>
    <li class="carousel-item"><img src="02.jpg" alt=""></li>
    <li class="carousel-item"><img src="03.jpg" alt=""></li>
  </ul>
  <div class="carousel-buttons">
    <a href="#" class="carousel-button active"></a>
    <a href="#" class="carousel-button"></a>
    <a href="#" class="carousel-button"></a>
  </div>
</div>

CSS代码：

.carousel {
  position: relative;
  width: 600px;
  height: 400px;
  margin: 0 auto;
}
.carousel-list {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  margin: 0;
  padding: 0;
  list-style: none;
  overflow: hidden;
}
.carousel-item {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  opacity: 0;
  transition: opacity 1s ease-in-out;
}
.carousel-item img {
  width: 100%;
  height: 100%;
}
.carousel-item.active {
  opacity: 1;
}
.carousel-buttons {
  position: absolute;
  bottom: 20px;
  left: 50%;
  transform: translateX(-50%);
}
.carousel-button {
  display: inline-block;
  width: 10px;
  height: 10px;
  margin: 0 10px;
  background-color: #ccc;
  border-radius: 50%;
}
.carousel-button.active {
  background-color: #f00;
}

JavaScript代码：

var carousel = document.querySelector('.carousel');
var carouselList = document.querySelector('.carousel-list');
var carouselItems = document.querySelectorAll('.carousel-item');
var carouselButtons = document.querySelectorAll('.carousel-button');
var currentIndex = 0;
var timer;

// 切换图片
function changeCarousel() {
  carouselItems[currentIndex].classList.remove('active');
  carouselButtons[currentIndex].classList.remove('active');
  currentIndex = (currentIndex + 1) % carouselItems.length;
  carouselItems[currentIndex].classList.add('active');
  carouselButtons[currentIndex].classList.add('active');
}

// 自动轮播
timer = setInterval(changeCarousel, 2000);

// 点击按钮切换图片
carouselButtons.forEach(function(button, index) {
  button.addEventListener('click', function(event) {
    event.preventDefault();
    clearInterval(timer);
    carouselItems[currentIndex].classList.remove('active');
    carouselButtons[currentIndex].classList.remove('active');
    currentIndex = index;
    carouselItems[currentIndex].classList.add('active');
    carouselButtons[currentIndex].classList.add('active');
    timer = setInterval(changeCarousel, 2000);
  });
});

// 鼠标悬停停止自动轮播
carousel.addEventListener('mouseover', function() {
  clearInterval(timer);
});

// 鼠标离开开始自动轮播
carousel.addEventListener('mouseout', function() {
  timer = setInterval(changeCarousel, 2000);
});