<div class="wrapper">
    <div id="header">
        <h1>CSS3 calc() Function</h1>
    </div>
    <div id="main">
        <h1>Far far away…</h1>
        <p>Far far away, behind the word mountains…</p>
    </div>
 
    <div id="accessory">
        <ul>
            <li><a href="#">Far far away…</a></li>
            <li><a href="#">Separated they live…</a></li>
            <li><a href="#">A small river named…</a></li>
        </ul>
    </div>
 
    <div id="footer">
        Visit the article…
    </div>
 
</div>

body {
    background: #E8EADD;
    color: #3C323A;
    padding: 20px; 
}
.wrapper {
    width: 1024px; /* Fallback for browsers that don't support the calc() function */
    width: -moz-calc(100% - 40px);
    width: -webkit-calc(100% - 40px);
    width: calc(100% - 40px);
    margin: auto; 
}
#header {
    background: #f60;
    padding: 20px;
    width: 984px;/*Fallback for browsers that don't support the calc() function*/
    width: -moz-calc(100% - 40px);
    width: -webkit-calc(100% - 40px);
    width: calc(100% - 40px);
}
#main {
    border: 8px solid #B8C172;
    float: left;
    margin-bottom: 20px;
    margin-right: 20px;
    padding: 20px;
    width: 704px; /* Fallback for browsers that don't support the calc() function */
    width: -moz-calc(75% - 20px * 2 - 8px * 2);
    width: -webkit-calc(75% - 20px * 2 - 8px * 2);
    width: calc(75% - 20px * 2 - 8px * 2); 
}
#accessory {
    border: 8px solid #B8C172;
    float: right;
    padding: 10px;
    width: 208px; /* Fallback for browsers that don't support the calc() function */
    width: -moz-calc(25% - 10px * 2 - 8px * 2 - 20px);
    width: -webkit-calc(25% - 10px * 2 - 8px * 2 - 20px);
    width: calc(25% - 10px * 2 - 8px * 2 - 20px);
}
#footer {
    clear:both;
    background: #000;
    padding: 20px;
    color: #fff;
    width: 984px;/* Fallback for browsers that don't support the calc() function */
    width: -moz-calc(100% - 40px);
    width: -webkit-calc(100% - 40px);
    width: calc(100% - 40px);
}