Use the "min-height" property
Be wary of paddings, margins and borders :)
html, body {
margin: 0;
padding: 0;
border: 0;
}
#B, #C, #D {
position: absolute;
}
#A{
top: 0;
width: 100%;
height: 35px;
background-color: #99CC00;
}
#B {
top: 35px;
width: 200px;
bottom: 35px;
background-color: #999999;
z-index:100;
}
#B2 {
min-height: 100%;
height: 100%;
margin-top: -35px;
bottom: 0;
background-color: red;
width: 200px;
overflow: scroll;
}
#B1 {
height: 35px;
width: 35px;
margin-left: 200px;
background-color: #CC0066;
}
#C {
top: 35px;
left: 200px;
right: 0;
bottom: 35px;
background-color: #CCCCCC;
}
#D {
bottom: 0;
width: 100%;
height: 35px;
background-color: #3399FF;
}