fixed定位

<!DOCTYPE html>
<html lang="en">
<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>
    html,body {
      height: 100%;
    }
    * {
      padding: 0;
      margin: 0;
      box-sizing: border-box;
    }
    #root {
      padding: 64px 0 0 200px;
      height: 100%;
    }
    header {
     
      position: fixed;
      top:0;
      left:0;
      height: 64px;
      border: 1px solid red;
      width: 100%;
      background: blue;
      z-index: 999;
    }

    nav {
      position: fixed;
      z-index: 998;
      top:0;
      left:0;
      width: 200px;
      border: 1px solid red;
      height: 100%;
      background: grey;
      padding-top: 64px;
    }

    main {
      background: pink;
      height: 100%;
    }
  </style>
</head>
<body>
  <div id='root'>
    <header>header</header>
    <nav>nav</nav> 
    <main>main</main>
  </div>
</body>
</html>

flex定位

<!DOCTYPE html>
<html lang="en">
<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>
    html,body,#root {
      height: 100%;
    }
    * {
      margin: 0;
      padding: 0;
    }
    #root {
      display: flex;
      flex-direction: column;
    }
    header {
      height: 64px;
      background: blue;
    }
    .container {
      flex: 1;
      display: flex;
      flex-direction: row;
    }
    nav {
      width: 200px;
      background: grey;
    }
    main {
      flex: 1;
      background: pink;
    }
  </style>
</head>
<body>
  <div id="root">
    <header>header</header>
    <div class="container">
        <nav>nav</nav>
        <main>main</main>
    </div>
  </div>
</body>
</html>

栅格布局

<!DOCTYPE html>
<html lang="en">
<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>
    html,body,#root {
      height: 100%;
    }
    * {
      margin: 0;
      padding: 0;
    }
    #root {
      
    }
    nav {
      width: 16%;
      height: 100%;
      float: left;
      background: grey;
    }
    main {
      width: 84%;
      height: 100%;
      float: left;
      background: pink;
    }
  </style>
</head>
<body>
  <div id="root">
    <nav>nav</nav>
    <main>main</main>
  </div>
</body>
</html>