| 123456789101112131415161718192021222324252627282930313233343536373839404142434445464748 | <!DOCTYPE html><html lang="en"><head>  <meta charset="UTF-8">  <meta http-equiv="X-UA-Compatible" content="IE=edge">  <meta name="viewport" content="width=device-width, initial-scale=1.0">  <title>Document</title>  <style>    *{      margin: 0;      padding: 0;    }    /* html{      font-size: 50px;    } */    #div1{      height: 200px;      background: red;      width: 3rem;      font-size: 100px;    }    #div2{      /* height: 100px; */      background: orange;      /* width: 2em; */      /* width: 10vw;      height: 10vh; */      width: 10%;      height: 10%;      /* vw vh  把视口分为100等分 根据输入的数字 去取多少 */    }    /* rem 是根据html的字体大小 */    /* em 是根据父元素的字体大小 */    #div3{      width: 100%;      height: calc(100vh - 100px);      background: blue;    }  </style></head><body>  <!-- <div id="div1">    <div id="div2"></div>  </div> -->  <div id="div3"></div></body></html>
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