float absolute

HTML

<div id="container">
    <div id="left"></div>
    <div id="main">
        
        <h1>test</h1>
    </div>
</div>

CSS

#container {
position:relative;
}
#left{
    float:left;
    width:200px;
    height:400px;
    background:#cfc;
}
#main{
    position:absolute;
    left:210px;
    right:0px;
    background:#f9c;
    height:400px;
   
}

h1{
    clear:both;    
}