<style type="text/css">
    *{
        margin: 0;
        padding: 0;
        box-sizing: border-box;
    }
    .container{
        width: 1000px;
        height: 1000px;
        margin: 100px;
        background-color: #f60;
    }
    .left{
       /*关键点在于将两个元素设置为display：table-cell*/
        display: table-cell;
        vertical-align: top;
        width: 20%;
        min-width: 200px;
        height: 400px;
        background-color: #ccc;
    }
    .right{
        display: table-cell;
        vertical-align: top;
        /*即使宽度设为2000px，元素的内容还是可以正常显示*/
        width: 2000px;
        height: 600px;
        background-color: #f10;
    }
</style>
<div class="container">
    <div class="left">left</div>
    <div class="right">right</div>
</div>