#red-box{
    position: absolute;
    top: 100px;
    left: 100px;
    width: 9px;
    height: 9px;
    background-color: red;
}

#blue-box{
    position: absolute;
    top: -100px;
    left: -100px;
    width: 9px;
    height: 9px;
    background-color: blue;
}

.red-box-tail{
    position: absolute;
    background-color: red;
    width: 9px;
    height: 9px;
}

#background{
    position: absolute;
    width: 300px;
    height: 300px;
    background-color: #6fa100;
}