With setting the padding values to Zero (0) – the padding-top is then:
/*** to quick css - better to place with the concerning page ID ***/
.mfp-iframe-holder {
padding: 0px !important;
}
.mfp-iframe-holder .mfp-content {
height: 90vh !important; /*** the wanted height ***/
width: 50.625vh; /*** the calculated width is then ***/
}
.mfp-iframe-scaler {
padding-top: 178%; /*** 100 x 16 / 9 = 177.88 ***/
}