.iframe-container {
  overflow: hidden;
  padding-top: 100%;
  position: relative;
}
 
.iframe-container iframe {
   border: 0;
   height: 100%;
   left: 0;
   position: absolute;
   top: 0;
   width: 100%;
}

.icon--landingpage { background-image: url(../images/topic-grey.png); }
.icon--book { background-image: url(../images/book.png); }
.icon--event { background-image: url(../images/event.png); }