来源：两分钟实现圆形放大效果，这个思路你一定要知道【渡一教育】

例如圆形头像，鼠标移入时以圆形从圆心向外逐渐变亮

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<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<style>
  /* 头像容器 */
  .avatar {
    width: 200px;
    height: 200px;
    margin: 200px auto;
    background-image: url(https://image.cheriko.fun/post/202306042214538.jpg);
    background-size: cover;
    background-position: center;
    border-radius: 50%;
    cursor: pointer;
    position: relative;
  }

  .avatar::before,
  .avatar::after {
    content: '';
    position: absolute;
    width: 100%;
    height: 100%;
    left: 0;
    top: 0;
    border-radius: 50%;
  }

  .avatar::before {
    background-color: rgba(0,0,0,.5);
  }

  .avatar::after {
    /* 获取父元素（这里是.avatar）的background */
    background: inherit;
    /* 裁剪元素 */
    clip-path: circle(0%);
    transition: 0.3s;
  }

  .avatar:hover::after {
    clip-path: circle(50%);

  }
</style>

<body>
  <div class="avatar">
  </div>
</body>

</html>

clip-path还可以裁剪出更多别的形状