利用transform实现一个纯CSS弹出菜单的示例代码

<nav>
  <ul>
    <li>
      <strong>home</strong>
      <div>
        <a href="">cms</a>
        <a href="">crm</a>
      </div>
    </li>
    <li>
      <strong>live</strong>
      <div>
        <a href="">java</a>
        <a href="">php</a>
      </div>
    </li>
    <li>
      <strong>pictrue</strong>
      <div>
        <a href="">mm</a>
        <a href="">dd</a>
      </div>
    </li>
  </ul>
</nav>

 *{
    padding: 0;
    margin: 0;
    box-sizing: border-box;
  }
  body{
    width: 100vw;
    height: 100vh;
    display: flex;
    flex-direction: column;
    justify-content: flex-start;
    align-items: center;
  }
  nav{
    margin: 10px;
  }
  nav ul {
    list-style-type: none;
    height: 32px;
    display: flex;
  }
  nav ul li{
    margin-right: 10px;
  }
  nav ul li strong{
    text-transform: uppercase;
    background-color: #9b59b6;
    color: white;
    padding: 5px 30px;
    line-height: 30px;
    cursor: pointer;
  }
  nav ul li strong+div{
    display: flex;
    flex-direction: column;
    background-color: #3498db;
    padding: 10px;
    transform: translateY(-110%);
    opacity: 0;
    transition: .3s;
    transform-origin: top;
  }
  nav ul li:hover div{
    transform: translateY(0);
    opacity: 1;
  }
  nav ul li strong+div a{
    color: white;
    text-decoration: none;
    text-transform: uppercase;
    padding: 5px 0;
  }