SOURCE

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

* {
        margin: 0;
        padding: 0;
    }
    .left{
        background: #73DE80;    /* 绿色 */
        opacity: 0.5;
        border: 3px solid #F31264;
        width: 200px;
        height: 200px;
        float: left;
    }
    .right{                        /* 粉色 */
        background: #EF5BE2;
        opacity: 0.5;
        border: 3px solid #F31264;
        width:400px;
        min-height: 100px;
    }
    .box{
        background:#888;
        height: 100%;
        margin-left: 50px;
    }