body {
    background: #555;
}

#conteneur {
    position: relative;
}

#conteneur > div {
    position: absolute;
    width: 5px;
    height: 5px;
}

#conteneur>div.GROUND {
    background-color: #666;
}
#conteneur>div.WALL {
    background-color: #000;
}
#conteneur>div.START {
    background-color: darkorange;
}

#conteneur>div.END {
    background-color: green;
}

#perso {
    background-color: red;
    z-index: 1;
    transition: all 0.01s;
}

#conteneur>div.evo {
    z-index: 1;
    background-color: red;
    opacity: 0.4;
}