#wrapper {
    height:400px;
    width:600px;
    position:absolute;
    bottom: calc(50% - 200px);
    right: calc(50% - 300px);
}

#rectangle {
    background-color: red;
    height: 100%;
    width: 100%;
    position:relative;
}

#carrebleu {
    position: absolute;
    bottom: 0;
    right: 0;
    background-color: blue;
    height: 200px;
    width: 200px;
}

#rond {
    position: absolute;
    bottom:0;
    left:0;
    background-color: yellow;
    height: 150px;
    width: 150px;
    border-radius:50%;
}

#carrevert {
    position:absolute;
    z-index: -1;
    top:-100px;
    right:-100px;
    background-color:green;
    height:200px;
    width:200px;
}