SOURCE

<div class="main">
    <div class="main-content">
      main content
    </div>
</div>
<div class="left">left</div>
<div class="right">right</div>

*{
        margin:0;
        padding: 0
    }
    .main{
        float: left;
        width: 100%;
      background-color:grey;

    }
    .main .main-content{
        margin: 0 210px;
        background-color: rgba(33, 114, 214, 0.8);
        height: 500px
    }
    .left{
        width: 200px;
        float: left;
        background-color: rgba(255, 82, 0, 0.8);
        margin-left: -100%;
        height: 200px

    }
    .right{
        width: 200px;
        height: 200px;
        margin-left: -200px;
        float: left;
        background-color: rgba(90, 243, 151, 0.8);
    }