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<head>
  <meta charset="UTF-8" />
  <meta name="viewport" content="Width = device - width, initial - scale = 1.0" />
  <meta http-equiv="X-UA-Compatible" content="ie=edge" />
  <title>Document</title>
  <style>
    .main {
      width: 100%;
      height: 100%;
      /* overflow: hidden; */
    }

    .head {
      width: 100%;
      height: calc(100px + 300px);
      background: yellow;
    }

    .left {
      background: red;
      width: 200px;
      overflow: scroll;
      float: left;
      height: calc(100% - 400px);
    }

    .right {
      background: green;
      margin-left: 200px;
      height: calc(100% - 400px);
      overflow: scroll;
    }

    html {
      width: 100%;
      height: 100%;
      /* overflow: hidden; */
    }

    body {
      width: 100%;
      height: 100%;
    }
  </style>
</head>

<body>
  <div class="main">
    <div class="head"></div>
    <div class="left"> 11111 1111111111111111111111111122222222222222222222222229999999999999999999999999999999999999999999999999999999999999999 11111111111111111111111111222222222222222222222222299999999999999999999999999999999999999999999999999999999999999 11111111111111111111111111222222222222222222222222299999999999999999999999999999999999999999999999999999999999999 11111111111111111111111111222222222222222222222222299999999999999999999999999999999999999999999999999999999999999 11111111111111111111111111222222222222222222222222299999999999999999999999999999999999999999999999999999999999999 11111111111111111111111111222222222222222222222222299999999999999999999999999999999999999999999999999999999999999 11111111111111111111111111222222222222222222222222299999999999999999999999999999999999999999999999999999999999999 11111111111111111111111111222222222222222222222222299999999999999999999999999999999999999999999999999999999999999 11111111111111111111111111222222222222222222222222299999999999999999999999999999999999999999999999999999999999999 11111111111111111111111111222222222222222222222222299999999999999999999999999999999999999999999999999999999999999 11111111111111111111111111222222222222222222222222299999999999999999999999999999999999999999999999999999999999999 11111111111111111111111111222222222222222222222222299999999999999999999999999999999999999999999999999999999999999 11111111111111111111111111222222222222222222222222299999999999999999999999999999999999999999999999999999999999999 11111111111111111111111111222222222222222222222222299999999999999999999999999999999999999999999999999999999999999 11111111111111111111111111222222222222222222222222299999999999999999999999999999999999999999999999999999999999999 11111111111111111111111111222222222222222222222222299999999999999999999999999999999999999999999999999999999999999 11111111111111111111111111222222222222222222222222299999999999999999999999999999999999999999999999999999999999999 11111111111111111111111111222222222222222222222222299999999999999999999999999999999999999999999999999999999999999 11111111111111111111111111222222222222222222222222299999999999999999999999999999999999999999999999999999999999999 11111111111111111111111111222222222222222222222222299999999999999999999999999999999999999999999999999999999999999 11111111111111111111111111222222222222222222222222299999999999999999999999999999999999999999999999999999999999999 11111111111111111111111111222222222222222222222222299999999999999999999999999999999999999999999999999999999999999 11111111111111111111111111222222222222222222222222299999999999999999999999999999999999999999999999999999999999999 </div>  <div class="right">
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</body>

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Knowledge:

1. Calc uses this function to calculate the height of an element to implement Overflow: Scroll

2. Children can inherit height only if the parent sets the height