#container {
  display: grid;
  grid-template-columns: 600px 600px 600px;
  grid-template-rows: 350px 350px 350px 350px 350px+
}

div { 
  display: table;
  height: 100px;
  width: 100px;
}

span{ 
  display: table-cell;
  border: solid 1px black;
  vertical-align: middle;
  text-align: center;
}

iframe {
  width: 560px;
  height: 315px;
}