SOURCE

 <div class="content">
    <div class="left">im left</div>
    <div class="main">im center</div>
    <div class="right"> im right</div>
  </div>

 *{
        padding: 0px;
        margin:0px;
    }
    .content{
        width: 100%;
        height:300px;
        display: flex;
    }
   .left{
        background-color: bisque;
        width: 200px;
   }
   .right{
       background-color:bisque;
       width: 200px;
   }
   .main{
       flex: 1;
       background-color: cadetblue;
   }