.matricula{
    font-size:40px;
    text-align:center;
    font-weight: bold;
}

#preview{
   width:500px;
   height: 500px;
   margin:0px auto;
}
@media screen and ( max-width : 899px ) and (min-width : 550px ){
    .codigoqr {
        width: 300px;
        height: 300px;
    }
    #preview {
        width: 300px;
        height: 300px;
    }
}

@media screen and ( max-width : 549px ) and (min-width : 350px ){
    .codigoqr {
        width: 250px;
        height: 250px;
    }
    #preview {
        width: 250px;
        height: 250px;
    }
    .imgadminlogin{
        width: 280px;
        height: 200px;
    }
}

@media screen and ( max-width : 349px ) and (min-width : 200px ){
    .codigoqr {
        width: 200px;
        height: 200px;
    }
    #preview {
        width: 200px;
        height: 200px;
    }
    .matricula{
        font-size:20px;
    }
    .imgadminlogin{
        width: 200px;
        height: 150px;
    }
}