SOURCE

<div class="header">header</div>
<div class="contain">
	<div class="main">main</div>

	<div class="left">left</div>

	<div class="right">right</div>

</div>
<div class="foot">foot</div>

.left {
    background-color: red;
    margin-left: -100%;
    width: 100px;
    left: -100px;
    position: relative;
}

.right {
    background-color: blue;
    margin-left: -100px;
    width: 100px;
    position: relative;
    right: -100px;
}

.main {
    background-color: green;
    width: 100%;
}

.left,
.right,
.main {
    float: left;
    height: 200px;
}

.header {
    background-color: pink;
}

.foot {
    background-color: yellow;
}

.contain::after {
    content: "";
    clear: both;
    display: block;
    padding: 0 100px;
}

.contain {
    padding: 0 100px;
}