.redirbloc
{
    position: absolute;
    text-align: center;
    position: center;
    background-color: black;
    border-left: 50px solid black;
    border-right: 50px solid black;
    border: 2px grey solid;
    border-radius: 15px 15px 12px 12px;
    padding:2%;
    opacity: 1;
      position: absolute; /* postulat de départ */
     top: 50%; left: 50%; /* à 50%/50% du parent référent */
     transform: translate(-50%, -50%); /* décalage de 50% de sa propre taille */
}

.imgcenter
{
      top: 50%; left: 50%;
}

@media screen and (max-width:999px) {
.redirpage {width:60%;}
.redirbloc {width: 60%; height:50%; padding-top: 3%;}
img {width: 50%; height: 50%}

@media screen and (max-width:800px) {
.redirpage {width:60%;}
.redirbloc {width: 60%; height:40%; padding-top: 7%;}
img {width: 50%; height: 50%}

@media screen and (max-width:350px) {
.redirpage {width:60%;}
.redirbloc {width: 60%; height:20%; padding-top: 7%;}
img {width: 50%; height: 50%}
}
}
}