body{
    background-color:blue;
    margin: 0;
    padding: 0;
}

#box1 {
    width:100%;
    height:50%;
    background-color:yellow;
    position:absolute;
}

#box2 {
    width:100%;
    height:25%;
    background-color:red;
    position:absolute;
    bottom:0px;
    padding:none;
}