布局例子

<header>header</header>
  <div id='main'>
      <article>article</article>
      <nav>nav</nav>
      <aside>aside</aside>
  </div>
<footer>footer</footer>
<style>
  body { font: 24px Helvetica; }
  #main {
    min-height: 500px;
    margin: 0px;
    padding: 0px;
    display: flex;
    flex-flow: row;
  }
  #main > article {
    margin: 4px;
    padding: 5px;
    border: 1px solid #cccc33;
    border-radius: 7pt;
    background: #dddd88;
    flex: 3 1 60%;
    order: 2;
  }
  #main > nav {
    margin: 4px;
    padding: 5px;
    border: 1px solid #8888bb;
    border-radius: 7pt;
    background: #ccccff;
    flex: 1 6 20%;
    order: 1;
  }
  #main > aside {
    margin: 4px;
    padding: 5px;
    border: 1px solid #8888bb;
    border-radius: 7pt;
    background: #ccccff;
    flex: 1 6 20%;
    order: 3;
  }
  header, footer {
    display: block;
    margin: 4px;
    padding: 5px;
    min-height: 100px;
    border: 1px solid #eebb55;
    border-radius: 7pt;
    background: #ffeebb;
  }
  /* 窄到已不足以支持三栏 */
  @media all and (max- 640px) {
    #main, #page {
      flex-direction: column;
    }
    #main > article, #main > nav, #main > aside {
      /* 恢复到文档内的自然顺序 */
      order: 0;
    }
    #main > nav, #main > aside, header, footer {
      min-height: 50px;
      max-height: 50px;
    }
  }
</style>