<div class="sidea"></div>
<div class="divb">
<div class="divc"></div>
</div>
.sidea {
width:150px;
background:red;
height:100px;
float:left;
}
.divb {
height:500px;
background:blue;
overflow:hidden;
}
.divc {
width:2000px;
background:green;
height:10px;
}