I dont know how to center a modal, I dont find an example to center vertically and horizontally my modal

    <div mdbModal #registro="mdbModal" class="modal fade left" id="registro" tabindex="-1" role="dialog"
    aria-labelledby="myModalLabel" aria-hidden="true">
    <div class="modal-dialog" role="document">
        <div class="modal-content mascara">
        <div class="modal-header text-center">
            <!--<h4 class="modal-title w-100 font-weight-bold">Registro</h4>-->
            <i class="fa fa-user ml-1  fa-2x color_verde2_um wow rotateIn" aria-hidden="true"></i>
            <h4 class="text-center mb-3 color_verde2_um m-auto ">Registro</h4>
            <button type="button" class="close" data-dismiss="modal" aria-label="Close" (click)="registro.hide()">
            <span aria-hidden="true">&times;</span>
            </button>
        </div>
        <div class="modal-body mx-3">
            <p class="card-text">
                ¡Únete al lugar donde encontrarás centralizada la información de la <strong>Universidad de Manizales</strong>!
            </p>
        </div>
        <div class="text-center mb-4">
            <hr>
            <button class="btn degradado-um btn-lg z-depth-1a waves-light" mdbWavesEffect (click)="fn_submitForm(formRegistro)">Ingresar<i class="fas fa-sign-in-alt ml-2"></i></button>
        </div>
        </div>
    </div>
    </div>