圣杯布局

<style>
  .container {
    width: 100vw;
    display: flex;
  }
  .main {
    background: red;
    flex-grow: 1;
    order: 2;
  }
  .left {
    background: #000;
    width: 200px;
    order: 1;
  }
  .right {
    background: blue;
    width: 200px;
    order: 3;
  }
</style>
<div class="container">
  <div class="main"></div>
  <div class="left"></div>
  <div class="right"></div>
</div>