/* Le code CSS de la démo */

article{
    width : 90%;
}

img{
    border: 10px solid green;
}

@media screen and (max-width:980px) {
    img{
    border: 10px solid red;
}
}
@media screen and (max-width:500px) {
    img{
    border: 10px solid blue;
}
}