#header
{
    height: 100px;
    width: 100%;
    background-color: red;
}

#content-shell
{
    position: absolute;
    top: 100px;
    bottom: 100px;
    width: 100%;
    background-color: blue;
}

#footer
{
    position: absolute;
    bottom: 0;
    height: 100px;
    width:100%;
    background-color: yellow;   
}