SOURCE

<header>双飞翼布局</header>
<div class="bd">
    <div class="main text">
        <div class="main-content">main</div>
    </div>
    <div class="left text">
        left
    </div>
    <div class="right text">
        right
    </div>
</div>
<footer>footer</footer>

header,footer {
    text-align: center;
    width: 100%;
    background-color: #bbbbbb;
}
.text {
    text-align: center;
    line-height: 200px;
    font-size: 40px;
    color: #fff;
}

.bd {
    overflow: hidden;
    height: 200px;
}

.main {
    float: left;
    width: 100%;
    background-color: #ddd;
}
.main-content {
    margin: 0 100px 0 200px;
}

.left {
    float: left;
    width: 200px;
    background-color: #da4242;
    /* 产生布局效果的属性 */
    margin-left: -100%;
}

.right {
    float: left;
    width: 100px;
    background-color: #4ddef1;
    /* 产生布局效果的属性 */
    margin-left: -100px;
}