style.css

body { background-color:whitesmoke; font-family: "Arial", sans-serif; }
.controls { background-color:lightgray; width:800px; padding:5px; }
button { background-color:rgb(149, 163, 204); border:none; text-align:center; padding:10px; margin:5px; }
button:hover { background-color: rgb(123, 134, 168); }
iframe { width:800px; height:600px; }
.slide { visibility:collapse; width:0px; height:0px; margin:0px; padding:0px; border:0px; }
.slide:fullscreen { visibility:visible; }
input { margin:5px; }

.dropdown {
  position: relative;
  display: inline-block;
}
.dropdown-content {
  display: none;
  position: absolute;
  background-color: whitesmoke;
  min-width: 130px;
  box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
  z-index: 1;
}
.dropdown:hover .dropdown-content { display:block; }
.dropdown:focus-within .dropdown-content { display:block; }