SOURCE

 <div class="box">
        <div class="left">测试</div>
    </div>

    <div class="box2">
        <div class="right">测试</div>
    </div>

 .box {
            border: 1px solid #f00;
            width: 100%;
            height: 100px;
        }
        .box2 {
            margin-top: 100px;
            border: 1px solid #f00;
            width: 100%;
            height: 100px;
        }
        .left {
            position: absolute;
            right: 0;
            left: 200px;
            border: 1px solid #0f0;        
        }
        .right {
            position: absolute;
            left: 0;
            right: 200px;
            border: 1px solid #0f0;    
            padding: 30px;
        }