iframe {
    border: 1px solid black;
    width: 815px;
    height: 470px;
}

.app {
    display: grid;
    grid-gap: 15px; 
    overflow: hidden;
  /*   grid-template-columns: repeat(auto-fill, 200px); */
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  /*   grid-template-columns: repeat(auto-fit, minmax(300px, 1fr) 150px); */
    grid-auto-flow: dense;
  }
  
.item {
  width: 240px;
  height: 120px;
  background-color:deepskyblue;
  cursor: pointer;
  text-align: center;
}

.item:nth-of-type(2n) {
  /*grid-column: span 2;*/
  background-color: darkolivegreen;
}

.item:nth-of-type(3n) {
  /*grid-column: span 2;*/
  background-color: royalblue;
}