.fullscreen-btn {
  position: absolute;
  bottom: 10px;
  right: 10px;
  background: rgba(0,0,0,0.7);
  color: #fff;
  border: none;
  font-size: 20px;
  padding: 8px 12px;
  border-radius: 6px;
  cursor: pointer;
  transition: background 0.3s;
}

.fullscreen-btn:hover {
  background: rgba(255,0,0,0.8);
}