body{
    margin: 0;
}
main{
    background-image: linear-gradient(powderblue, hotpink, lavender, magenta, turquoise);
    display: grid;
    grid-template-columns: 1fr 1fr 1fr 1fr;
    grid-template-rows: 1fr 1fr 1fr 1fr 1fr;
    gap: 1rem;
    padding: 1rem;
    box-sizing: border-box;
  }

  div{
      background-color: whitesmoke;
      padding-top: 75%;
      position: relative;
      overflow: hidden;
      transition-duration: 1000ms;
      transition-timing-function:
  }

  a {
    display: block;
    position: absolute;
    /* padding-top: 100%; */
  }

  a:after {
    content: '';
    position: absolute;
    background-color: yellow;
    opacity: 0.0;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: 5;
  }

  /* iframe {
    border: 2px solid blue;
    display: block;
    display: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: 5;
  } */

  iframe {
    width: 100%;
    height: 100%;
    position: absolute;
    border: 0;
  }

  .preview {
    position: absolute;
    top: 0;
    min-height: 100%;
    width: 100%;
    z-index: 6;
    padding-top: 0%;
  }
  div:hover{
    filter: hue-rotate(180deg);
  }