body {
  font-family: Arial, sans-serif;
  margin: 0;
  background-color: #000;
  color: #f00;
}
header {
  background-color: #111;
  padding: 20px;
  text-align: center;
}
main {
  padding: 20px;
}
.selector {
  margin-bottom: 20px;
}
.viewer iframe {
  width: 100%;
  height: 400px;
  background: #222;
  border: 2px solid #f00;
}
.assistant {
  margin-top: 20px;
  padding: 10px;
  background: #111;
  border: 1px solid #f00;
}