SOURCE

<div class="container">
    <div class="center">center</div>
    <div class="left">left</div>
    <div class="right">right</div>
</div>

.container {
    height: 400px;
    overflow: hidden;
}

.center {
    float: left;
    background-color: aqua;
}
.left {
    float: left;
    width: 200px;
    background-color: #f00;
}
.right {
    float: right;
    width: 200px;
    background-color: #ff0;
}