<!DOCTYPE HTML>
<head>
  <style>
    .parent {
       width: 200px;
       height: 200px;
       isolation: isolate;
    }
    .child {
      width: 200px;
      height: 200px;
      background: green;
    }
  </style>
</head>
<body>
 <div class="parent">
  <div class="child">
  </div>
 </div>
</body>