.responsive-iframe {
    position: relative;
    padding-bottom: 56.25%;
    /* 16:9 aspect ratio */
    height: 0;
    overflow: hidden;
    max-width: 100%;
    background: #000;
    /* optional */
    border-radius: 8px;
    /* optional */
  }

  .responsive-iframe iframe {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    border: 0;
  }