Bootstrap4 轮播

<div id="demo" class="carousel slide" data-ride="carousel">
 
  <!-- 指示符 -->
  <ul class="carousel-indicators">
    <li data-target="#demo" data-slide-to="0" class="active"></li>
    <li data-target="#demo" data-slide-to="1"></li>
    <li data-target="#demo" data-slide-to="2"></li>
  </ul>
 
  <!-- 轮播图片 -->
  <div class="carousel-inner">
    <div class="carousel-item active">
      <img src="https://static.runoob.com/images/mix/img_fjords_wide.jpg">
    </div>
    <div class="carousel-item">
      <img src="https://static.runoob.com/images/mix/img_nature_wide.jpg">
    </div>
    <div class="carousel-item">
      <img src="https://static.runoob.com/images/mix/img_mountains_wide.jpg">
    </div>
  </div>
 
  <!-- 左右切换按钮 -->
  <a class="carousel-control-prev" href="#demo" data-slide="prev">
    <span class="carousel-control-prev-icon"></span>
  </a>
  <a class="carousel-control-next" href="#demo" data-slide="next">
    <span class="carousel-control-next-icon"></span>
  </a>
 
</div>

<div class="carousel-item">
  <img src="https://static.runoob.com/images/mix/img_fjords_wide.jpg">
  <div class="carousel-caption">
    <h3>第一张图片描述标题</h3>
    <p>描述文字!</p>
  </div>
</div>