#divPrincipal {
    width: 90%;
    margin: 0 auto;
}

#banner {
    margin-left: auto;
    margin-right: auto;
    width: 90%;
    text-align: center;
}

html, body {
    box-sizing: border-box;
}

*, *:before, *:after {
    box-sizing: inherit;
  }

.contenedorTarjetas {
    margin-top: 30px;
    width: 100%;
    padding: 0px;
}

.tarjeta {
    border: 1px solid #000000;
    display: inline-block;
}

.tarjetaUnTercio {
    width: 33%;
}

.tarjetaUnCuarto {
    width: 24%;
}

.imagenAnchoCompleto {
    width: 100%;
}