#problem, #answer, #hint {
  border: 1px solid #ccc;
  border-radius: 8px;
  padding: 8px 12px;
  margin: 10px 0;
  background: #fafafa;
}
button.btn {
  background: #4caf50;
  color: white;
  border: none;
  padding: 6px 12px;
  border-radius: 6px;
  cursor: pointer;
}
@media screen and (min-width: 960px) {
   img {
    max-width: 60vw;
  }
}
button:hover {
  background: #45a049;
}