SOURCE

<div class="header">header</div>
<div class="content">
     <div class="comuln" id="center">center</div>
    <div class="comuln" id="left">left</div>
    <div class="comuln" id="right">right</div>
</div>
<div class="footer">footer</div>

.header,
.footer {
    border: 1px solid red;
    text-align: center;
    height: 50px;
    line-height: 50px;
}

.content {
    border: 1px solid green;
    margin: 10px 0;
}

.left {
    width: 300px;
    background-color: saddlebrown;
}

.center {
    width: 100%;
    background-color: red;
}

.right {
    width: 200px;
    background-color: skyblue;
}

.comuln {}