#div1 {
float: left;
background: blue;
color: white;
height:100%;
width:200px;
}

#div2{
height: 100%;
background: yellow;
color: blue;
margin-right:200px;
width:100%;
}
#all{
width:100%;
}

HTML

<div id=«all»>
<div id=«div1»> Content1 </div>
<div id=«div2»>Content2 </div>
</div>