html {
    display: flex;
    height: 100%;
}

body {
    display: flex;
    height: 100%;
    flex-direction: column;
    flex-grow: 1;
    justify-content: center;
    align-items: center;
}

iframe {
    width: 80%;
    height: 900px; /* change this value to adjust the height as desired */
  }