display: box;

by goropoo

HTML

<div id="container">
    <div id="main">main</div>
    <div id="leftBox">leftBox</div>
    <div id="rightBox">rightBox</div>
</div>

CSS

#container {
    width: 100%;
    display: -webkit-box;
    display: -moz-box;
}
#main {
    -webkit-box-flex: 1;
    /* Safari,Google Chrome用 */
    -moz-box-flex: 1;
    /* Firefox用 */
    background: #EEE;
    min-height: 500px;
    -webkit-box-ordinal-group: 2;
    -moz-box-ordinal-group: 2;
}
#leftBox {
    width: 250px;
    background: #999;
    min-height: 300px;
    -webkit-box-ordinal-group: 1;
    -moz-box-ordinal-group: 1;
}
#rightBox {
    width: 250px;
    background: #666;
    min-height: 100px;
    -webkit-box-ordinal-group: 3;
    -moz-box-ordinal-group: 3;
}