A CodePen by Liam.

index.html

<div id="wrapper">
<div id="header"></div>

<div id="left"></div>
<div id="middle"></div>
<div id="right"></div>

<div id="footer"></div>
</div>

style.css

* {
padding: 0px;
margin: 0px;
}

#wrapper {
width: 100%;
}

#header {
width: 100%;
height: 200px;
background: lightgreen;
}

#left {
width: 20%;
height: 400px;
background: blue;
float: left;
}

#middle {
width: 60%;
height: 400px;
background: orange;
float: left;
left: 20%;
}

#right {
width: 20%;
height: 400px;
background: yellow;
float: left;
left: 80%;
}

#footer {
width: 100%;
height: 100px;
background: green;

clear: both;
}