div{
    width: 100%;
    height: 100px;
    background-color: orange;
    margin: 0 auto 20px auto;
    border: 2px solid black;
    box-sizing: border-box;
}
.d1{
    animation-name: couleur;
    animation-duration: 2s;
}
.d2{
    animation-name: couleur;
    animation-duration: 5s;
}
.d3{
    animation-name: couleur;
    animation-duration: 10s;
}
@keyframes couleur{
    from{background-color: orange;}
    50%{background-color: purple;}
    to{background-color: orange;}
}