@media screen and (max-width: 990px) {
    .item{}
    #primero{
        background-image: url('../imagenes/mov2.png') ;
        background-repeat: no-repeat;
        background-size: auto;
    }
    #second{
        background-image: url('../imagenes/mov6.png');
        background-repeat: no-repeat;
        background-size: auto;
    }
    #tercero{
        background-image: url('../imagenes/mov31.11.1.png');
        background-repeat: no-repeat;
        background-size: auto;
    }


}