效果说明:
当用户鼠标点击搜索输入框,可以显示预设商品信息,移除鼠标就隐藏内容,主要的思路是修改resultList里的原display样式none为block;


<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>小米搜索框显示隐藏案例</title>
  <style>
    * {
      margin: 0;
      padding: 0;
      box-sizing: border-box;
    }
    ul {
      list-style: none;
    }
    .mi {
      position: relative;
      width: 223px;
      margin: 100px auto;
    }
    .mi .search-text {
      width: 223px;
      height: 48px;
      padding: 0 10px;
      font-size: 14px;
      line-height: 48px;
      border: 1px solid #e0e0e0;
      outline: none;
    }
    /* 搜索框边框颜色 */
    .mi .search {
      border: 1px solid #ff6700;
    }
    /* 下拉菜单 */
    .result-list {
      position: absolute;
      left: 0;
      top: 48px;
      display:none;
      width: 223px;
      border: 1px solid #ff6700;
      border-top: 0;
      background: #fff;
    }
    .result-list a {
      padding: 6px 15px;
      font-size: 12px;
      color: #424242;
      text-decoration: none;
    }
    .result-list a:hover {
      background-color: #eee;
    }
  </style>
</head>
<body>
  <div class="mi">
    <input type="search" placeholder="小米笔记本" class="search-text">
    <ul class="result-list">
      <li><a href="#">全部商品</a></li>
      <li><a href="#">小米11</a></li>
      <li><a href="#">小米10S</a></li>
      <li><a href="#">小米笔记本</a></li>
      <li><a href="#">小米手机</a></li>
      <li><a href="#">黑鲨4</a></li>
      <li><a href="#">空调</a></li>
    </ul>
  </div>
  <script>
const searchText = document.querySelector('.search-text')
const resultList = document.querySelector('.result-list')
// resultList.style.display='none'
searchText.addEventListener('focus',function(){
  resultList.style.display='block'
  searchText.classList.add('search')
})

searchText.addEventListener('blur',function(){
resultList.style.display='none'
  searchText.classList.remove('search')
})
  </script>
</body>

</html>