corner.html

<!DOCTYPE html>
<html>
<head>
  <title>corner圆角布局</title>
  <style type="text/css">
    body {
      background-color: #000;
    }
    .corner {
      position: fixed;
      width: 100px;
      height: 100px;
      background-color: #fff;
      border-radius: 50%;
      transition:width 2s, height 2s, left 2s, top 2s, right 2s, bottom 2s
    }

    .corner:hover{
      width: 200px;
      height: 200px;
    }
    .corner.left {
      left: -50px;
    }

    .corner.left:hover{
      left: -100px;
    }

    .corner.right {
      right: -50px;
    }

    .corner.right:hover {
      right: -100px;
    }

    .corner.top {
      top: -50px;
    }

    .corner.top:hover {
      top: -100px;
    }

    .corner.bottom {
      bottom: -50px;
    }
    .corner.bottom:hover {
      bottom: -100px;
    }

    .circle{
      position: fixed;
      width: 100px;
      height: 100px;
      border-radius: 50%;
      background-color: #fff;
      left: 50%;
      top: 50%;
      margin-left: -50px;
      margin-top:-50px;
      transition: width 2s, height 2s, margin 2s
    }

    .circle:hover{
      width: 200px;
      height: 200px;
      margin-left: -100px;
      margin-top:-100px;
    }
  </style>
</head>
<body>
<div class="corner left top"></div>
<div class="corner left bottom"></div>
<div class="corner right top"></div>
<div class="corner right bottom"></div>
<div class="circle"></div>
</body>
<html>