body {
  margin: 0;
  overflow: hidden;
  background: black;
  font-family: sans-serif;
}

#overlay {
  position: fixed;
  top: 0; left: 0;
  width: 100%; height: 100%;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  background: rgba(0,0,0,0.8);
  color: white;
  z-index: 10;
}

button {
  padding: 1em 2em;
  font-size: 1.1em;
  border: none;
  border-radius: 8px;
  cursor: pointer;
}

.hidden { display: none; }

.spinner {
  width: 50px;
  height: 50px;
  border: 6px solid #ddd;
  border-top: 6px solid #09f;
  border-radius: 50%;
  animation: spin 1s linear infinite;
  margin-bottom: 1em;
}

@keyframes spin {
  from { transform: rotate(0deg); }
  to { transform: rotate(360deg); }
}