两列布局两种方法实现

<style>
        .box1{
            width: 200px;
            height: 100px;
            float: left;
            background: blue;
            margin-left: -100%;
        }
        .box2{
            width: 100%;
            float: left;
            height: 100px;
            background: red;
        }
        .box3{
            width: 100%;
            height: 100px;
            background: yellow;
            float: left;
        }
        .box2_wrap{
            margin-left: 200px;
        }
    </style>
<div id="container">
        <div class="box2">
            <div class="box2_wrap">box2</div>
        </div>
        <div class="box1">box1</div>
        <div class="box3">box3</div>
    </div>