html,
body {
  margin: 0;
  padding: 0;
  height: 100%;
  overflow: hidden;
  background: #0b0c10; /* default blackish */
  touch-action: none;
}

#c {
  position: fixed;
  inset: 0;
  width: 100vw;
  height: 100vh;
  display: block;
}

#topbar {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;

  display: flex;
  gap: 10px;
  padding: 10px;

  z-index: 10;
  pointer-events: auto;

  /* subtle overlay */
  background: rgba(11, 12, 16, 0.55);
  backdrop-filter: blur(6px);
}

#topbar button {
  flex: 1;
  padding: 12px 10px;
  border-radius: 12px;
  border: 1px solid rgba(255, 255, 255, 0.18);
  background: rgba(255, 255, 255, 0.08);
  color: #e5e7eb;
  font-size: 16px;
}