main

/* stylesheet */
.right1 {float:right; width:10em; height:600px; background:#def;}
.right2 {float:right; width:10em; height:600px; background:#ff9;}
.main   {width:auto; height:600px; background:#cf9;}

<!--source-->
<div class="right1">right1</div>
<div class="right2">right2</div>
<div class="main">main</div>